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Tuatara: Volume 2, Issue 2, July 1949

A Guide to the Oxyrhyncha, Oxystoma and Lesser Crabs

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A Guide to the Oxyrhyncha, Oxystoma and Lesser Crabs

The Brachyura is divided into five main groups, of which only the Brachygnatha is well-represented in our known fauna. The Brachygnatha includes the Brachyrhyncha which contains the bulk of the common crabs of the exposed fore-shore, and the Oxyrhyncha, few of which inhabit tidal levels. The majority of the oxyrhynchs is to be collected by dredging and accordingly most have been rarely taken here; but careful search of beaches, of wrack, etc., after storms, the examination of pools exposed at the lowest of tides, and of the weeds, etc., on the bottom of dry-docked ships, will yield a reasonably representative collection. The Oxystomata is not well represented, and our species are known only from sub-tidal levels. The Dromiacea is known from the one species. The Hapalocarcinidea contains crabs which are parasitic or symbiotic in corals, the coral forming a shell-like den in which the crab probably lives permanently. So far, this small group is unknown for our waters, and no representative of the primitive Gymnopleura has yet been recorded although both groups are known from the Indian and Pacific oceans (see p. 69).

The Oxyrhyncha includes the Parthenopidae, known here from the one species Eurynolambrus australis which is common among stones in the lower tidal region; the Majidae, masking crabs, of which only Paramithrax latreilli and P. minor are found in tidal pools, although P. peronii is occasionally found at the lowest tides; and the Hymenosomidae. The upper margin of the orbit is of great systematic value for the Majidae where it consists of three parts: a preorbital, a median orbital, and a postorbital. These may be spine-like, tooth-like, or in the form of a flange. Individually or collectively they may shield the eye or if spaced out or weakly developed, the eye and the stalk may be exposed. In Paramithrax, the three segments are spaced out and the eye when pressed back does not reach to the postorbital spine, as it does in Leptomithrax where the three segments are crowded together so that when the eye is pressed backwards the eye-stalk is concealed and the cornea reaches to the postorbital spine. For this reason it is necessary to transfer Thomson's Paramithrax longipes to the g. Leptomithrax. Balss (1929, Senckenbergiana, v. ii) has transferred Prionorhynchus edwardsii to the g. Jacquinotia and described a new genus for Campbellia kohli a new species from Campbell Island which may occur here.

This study has been assisted by a grant-in-aid of research from the Research Grant Committee of the University of New Zealand. page 59

The Hymenosomidae are not well known, which is unfortunate since these small crabs occur in variety and numbers and can be readily collected. A search at low tide in Zostera and Ulva in pools on mud-flats will produce a variety of species which have caused much trouble to systematists. The difficulties are several since there is no orbit, the carapace lacks ornamentation, etc., but chiefly the difficulties are the result from neglect. Bennett promised a monograph but though completed it has not been published. Originally the genera listed for our waters were Hymenosoma, Hymenicus, Halicarcinus and Elamena, together including some fifteen species. Montgomery (1931, Journ. Linn. Soc., v. 37) shows that the Hymenosoma depressum of Jacquinot and Lucas cannot belong to Hymenosoma since the original specimens have an epistome, and it seems best here to return the species to the early-proposed and apparently still valid g. Hombronia. The sole available specimen (from the Dominion Museum) although incomplete shows the remarkable plate described in the key on the right side but it appears to have been removed from the other. Balss (1929) has re-examined the types of Halicarcinus huttoni and shown this species to be a synonym of H. ovatus; Gordon (1940, Proc. Linn. Soc. Lond. No. 152 (1)) reports that the types of Elamena whitei belong to Halicarcinus. Chilton concluded that H. tridentatus is a variety of H. planatus, while Bennett regarded H. tridentatus as a complex of species. Fortunately Rathbun and also Balss have examined New Zealand material and recognised H. planatus from these waters. All available material I have examined is referable without difficulty to either H. planatus or to H. ovatus. So far, H. tridentatus in one form or another, has not been recognisable. Chilton's H. marmoratus is not recognisable from the published description. Since he considered it a possible synonym of H. varius, the original specimen may be referable to H. cooki or to the species (Key, 15) which is common but not yet referable to a named species. All of my material of this family belong either to Halicarcinus or Elamena, and it is probably adequate to follow Kemp's decision (1917, Rec. Ind. Mus. v. xiii), to include Hymenicus in Halicarcinus.

The Oxystomata contains three families, of which only the Leucosiidae is known to be represented in our waters. A box-crab (Calappa hepatica) was listed by Ortmann but has not been reported again in the fifty and more years since the first account. Four species of Ebalia have been reported. Only the one species is known to me. This is characterised by the presence of a minute lateral spine; a more or less acute spine at each end of the posterior margin; a larger more prominent, obtuse, rounded spine on the median line extending beyond and overhanging the posterior margin, so that in dorsal view there appear to be three posterior lobes; and a row of minute teeth on the posterior margin of the arm. The ten specimens in my collection show a marked variation on the dorsum of the carapace which ranges from the appear- page 60 ance of being agranular, to completely granular, and also shows variation in the degree of development of tubercles which in the better developed cases appear as two prominent tubercles on either side of the gastric region, one on each branchial region, and two others forming a circle with a sixth tubercle situated on the middle of the intestinal region at the centre of the circle. These tubercles are not obvious in some specimens. It is quite probable that Kirk and Chilton's records of E. laevis, Kirk's record of E. tumefacta, and the several records of E. tuberculosa, may all refer to this species in one variation or another. Certainly my material from the southern Sounds and Cook Strait is all referable to E. cheesemani.

The Dromiacea are known to me only by one specimen of Petalomera lateralis (formerly Cryptodromia) but the group is well represented in Australian waters and other species will probably be found here when our offshore waters are explored.

I must record my great debt to Mr. Abernethy who, as engineer on several trawlers, has saved specimens for me. He has collected several new and some rare species which will be described elsewhere. Unless otherwise acknowledged, the figures are drawn from specimens, some on loan from the Dominion Museum and other Museums, but mostly in my own collections. The figures have been prepared by Miss S. Krefft, whose assistance in this and many other ways, has greatly facilitated the construction of this guide. The figures are not drawn to scale and ornamentation is commonly omitted. Plate and figure numbers continue from the previous article. The essential morphology can be largely obtained from a study and dissection of the crayfish; but comparative crab material is necessary for an appreciation of the anatomy of the orbit.

Key To The Major Sub-Divisions Of Brachyura

1 (10) Generally crab-like; the cephlothorax more or less as wide or wider than long and the branchiostegite complete above the posterior legs; posterior region of thoracic sternum, flat, not keel-like.
2 (3) Mouth-field longer than wide, triangular, narrowing anteriorly to form a gutter-like buccal cavern; epistome much reduced, often absent. OXYSTOMATA.
3 (2) Mouth-field more or less as long as wide; squarish or oblong.
4 (9) Buccal cavern covered by external maxillipeds, as is usual.
5 (8) Last pair of thoracic legs normal, not arising from a dorsal or sub-dorsal position; flagellum of antenna very short. BRACHYGNATHA.
6 (7) Front very narrow, commonly with a distinct rostrum; either: orbits formed, body broadly triangular, or pear-shaped and
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inflated over hepatic region; or: orbits lacking, carapace ovoidal to circular and dorsum membranous and flat. OXYRHYNCHA.
7 (6) Front wide; rostrum reduced or commonly absent; body transversely square, oval, or if round not membranous; orbits formed, commonly complete. BRACHYRHYNCHA. (See “Tuatara,” Vol. II, p.29.)
8 (5) Last pair of thoracic legs subdorsal, relatively small; antenna long, flagellum equal or exceeding half width of carapace. DROMIACEA. (Sole known representative Petalomera lateralis. (Fig 51)) (Low-tide level and offshore in deeper water; ½ inch wide.)*
9 (4) External maxillipeds narrow and fail to cover the very wide buccal cavern. HAPALOCARCINIDEA. (Apparently as yet not known from these waters.)
10 (1) Carapace elongate, flattened or sub-cylindrical (rather as in the crayfish) and the branchiostegite emarginate to expose wall of thorax above the posteriar legs; posterior thoracic sternites narrow, keel-like; mouth-field commonly elongate, the sides parallel. GYMNOPLEURA. 1.

Key to the Families of Oxyrhyncha

1 (4) Carapace not thin and flat; chelipeds mobile and powerful, with bent fingers; orbits usually present.
2 (3) Orbits generally more or less incomplete; chelipeds especially mobile, rarely much greater than legs or rarely having fingers bent at an angle to hand; hooked hairs nearly always present. MAJIDAE. (Masking crabs; spider crabs.)
3 (2) Orbits well-made; chelipeds not especially mobile, usually much longer and heavier than legs and with fingers usually bent at an angle to the hand in the direction of the fixed finger; hooked hairs rarely present. PARTHENOPIDAE. (Known from one species, as follows: carapace much broader than long, nearly flat, rugose above with four major depressions; front very narrow. Eurynolambrus australis. (Fig 38.) (Low tidal and below; rocky beaches; up to 1 ¾ inches long.)
4 (1) Carapace thin and flat; chelipeds not long or bent; no orbits; no hooked hairs. HYMENOSOMIDAE. (Flat-back crabs.)

Key to the Species of Majidae

1 (7) Eye-stalks exposed, commonly long and non-retractile; orbits lacking. (Sub-F. Inachinae.)
2 (5) Basal joint of antenna not fused to surrounding parts, and its ventral face convex; merus of external maxillipeds narrower
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Figs. 24, Echinomaia hispida (Inset, chela); 25, Naxia buttoni (Inset, last walking leg); 26, Jacquinotia edwardsii; 27, Acanthophrys filholi; 28, Paramicippa spinosa; 29, Campbeljia kohli; 30, Leptomithrax sternocostulatus; 31, L. longipes; 32, L. australis; 33, L. longimanus; 34, Paramithrax latreilli; 35, P. peronii; 36, P. minor; 37, P. parvus; 38, Eurynolambrus australis. (Figs. 24, 37, after Borradaile; 27, after Filhol; 28, after Miers; 29, after Balss; 30, after Grant and McCulloch.)

Figs. 24, Echinomaia hispida (Inset, chela); 25, Naxia buttoni (Inset, last walking leg); 26, Jacquinotia edwardsii; 27, Acanthophrys filholi; 28, Paramicippa spinosa; 29, Campbeljia kohli; 30, Leptomithrax sternocostulatus; 31, L. longipes; 32, L. australis; 33, L. longimanus; 34, Paramithrax latreilli; 35, P. peronii; 36, P. minor; 37, P. parvus; 38, Eurynolambrus australis.
(Figs. 24, 37, after Borradaile; 27, after Filhol; 28, after Miers; 29, after Balss; 30, after Grant and McCulloch.)

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than ischium, the palp large and the whole appendage somewhat pediform.
1433 (4) Carapace elongate-triangular, inflated; rostral spines short, acute; gastric region with a short blunt spine and two tubercles forming a triangle. (Stenorhynchus fissifrons.) (Known for New Zealand only from one specimen in the McLeay Museum, Sydney.)
1434 (3) Carapace nearly circular, as broad as long; nine large spines on carapace; lacking hooked hairs. Echinomaia hispida (Fig. 24). (Known from two specimens; offshore; sand bottom; ½ inch long.)
1435 (2) Basal joint of antenna fused to surrounding parts, ventral face flattened or concave; merus of external maxillipeds as broad or broader than ischium, and the palp small.
1436 (-) Rostral spines each with a ventral spinule; antero-lateral borders spinous; walking legs sub-chelate. Naxia huttoni (Fig. 25) Sub-littoral and offshore waters, among stones and weeds; carapace and legs with strong hairs; everywhere covered with a fine fur; up to 3 ½ inches long.)
1437 (1) Eye-stalks more or less concealed and retractile.
1438 (16) Orbits never sufficiently complete to entirely conceal cornea of retracted eye; eye-stalks more or less concealed or concealable by a preocular or postocular spine; eye-stalks may be short or obsolete, or sunk into rostrum.
1439 (11) No true orbits; eye-stalks little movable, short and concealed by a supraocular spine, or sunk into rostrum. (Sub-F. Acanthonychinae.)
14310 (-) Rostrum laterally compressed and flanked by salient supraocular spines; carapace smooth; antero-lateral borders with a sharp anterior process at the base of the rostrum and one (male, bilobed) or two (female, anterior bilobed, posterior trilobed) processes on postero-lateral border. (Huenia bifurcata.) (Known only from type specimen for New Zealand.)
14311 (9) Orbits present; eyes retractile into a large cupped recess on postocular processes but leaving cornea at least partly visible. (Sub-F. Pisinae.)
14312 (13) Rostrum of rounded dentate lobes, directed obliquely downwards; carapace with numerous small rounded tubercles interspersed with larger ones some of which form a longitudinal median series; antero-lateral margins, spinous; body wider with age. Jacquinotia edwardsii. (Fig. 26) (Two fathoms and deeper; apparently southern; up to 4 inches wide.)
14313 (12) Rostrum of two divergent spines.
14314 (15) Antero-lateral margins straight, long, unarmed; a prominent lateral spine; rostral spines very long, ½ to 2/3 width of cara-
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pace which is polished when denuded and has a single midgastric tubercle; everywhere with stiff curling hairs. (Hyastenus (= Halimus) diacanthus.) (Offshore; up to 2 ¼ inches long.)
14315 (14) Antero-lateral margins lamellate, divided into lobes; rostral spines, long; carapace, hairy. Acanthophrys filholi. (Fig 27) (Offshore; inadequately known; 2 inches long.)
14316 (8) Orbits more or less complete, either: complete enough to entirely conceal cornea of retracted eye in dorsal view; or: the eyes partially protected by an antler-like supraocular spine, or by a jagged postocular tooth, or both (Sub-F. Majinae.)
14317 (18) Rostrum very broad, lamellate, deflexed forming a transversely oblong plate, two-lobed and crenulate on the anterior margin; carapace granulous; antero-lateral margin, spinous; orbital floor complete. (Paramicippa spinosa) (Fig. 28) (Offshore; ¾ inch long.)
14318 (17) Rostrum incised more or less deeply into two triangular lobes or two long spines.
14319 (20) Rostrum of two flattened divergent broad spines with toothed margins; legs strongly spinous; orbital floor complete. Campbellia kohli. (Fig. 29) (Known from one male, Campbell Island; offshore; ½ inch long.)
14320 (19) Rostrum of two rounded elongate spines; orbital floor incomplete.
14321 (30) Postorbital segment closely approximated to the median element in the dorsal margin of the orbit and cupped to receive and concealing much of the eye when pressed back; wrist without ridges, often granulous. G. Leptomithrax.
14322 (23) Postorbital segment elongate oblong, not spiniform, distally truncate, the extremity, bidentate; in the male, thoracic sternites each with a definite deep rimmed pit on either side of the abdomen. (L. sternocostulatus.) (Fig 30) (Offshore; up to 1 ½ inches long.)
14323 (22) Postorbital segment a spine.
14324 (25) Wrist without granules; cheliped barely as long as first walking leg. L. affinis. (Offshore; known from one specimen 1 ¾ inches long, indistinguishable from the female of L. longimanus excepting for the wrist.)
14325 (24) Wrist with granules.
14326 (27) External maxillipeds clothed with a short fur but leaving a prominent naked, white, circular patch on the outer face; definite rimmed pits in each sternite on either side of abdomen in the male; median orbital spine almost excluded from the rim of orbit by the anterior and posterior lobes which nearly meet lateral to it. L. longipes. (Fig. 31) (Offshore; up to 2 inches long.)
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27(26) External maxillipeds clothed or naked, but always lacking a naked central disc; sternal pits if present shallow and rimless.
28(29) Granules restricted to upper and outer surfaces of arm and wrist; postorbital spine with an accessory spinule on medial margin; rostral spines short, scarcely divergent; antero-lateral spines as long or longer than postorbital; fixed finger fully denticulate. L. australis. (Fig. 32) (Offshore; up to 2 ½inches long.)
29(28) Granules on all surfaces of arm and wrist; no accessory spine on postorbital; rostral spines long; fixed finger denticulate only on distal half; antero-lateral spines low, not as large as post-orbital. L. longimanus. (Fig. 33) (Offshore; up to 1 ½ inches long.)
30(21) The postorbital segment a simple uncupped spine remote from the eye when pressed back; wrist with longitudinal ridges, usually one on the upper face and one obliquely crossing the outer face. G. Paramithrax.
31(32) Lacking spines on the mid-dorsal line of the carapace which is covered in all regions with piliferous rounded tubercles; six prominent acute spines posterior to the postorbital; arm with a crest of strong spines on the dorsal aspect. P. latreilli. (Fig. 34) (Common in pools on rocky and stony beaches; up to 2 ½ inches long.)
32(31) A row of spines situated on the median dorsal line of the carapace.
33(34) Five (occasionally four) large well-spaced spines on the branchial margin; rostral spines strongly divergent; several large spinous tubercles on arm. P. peronii. (Fig. 35) (Lower tidal levels on rocky and stony beaches; offshore on sand; up to 3 inches.)
34(33) A row of seven small spines, more or less crowded, extending onto the dorsum of the branchial region.
35(36) Rostral spines long, about 1/5th the length of the rest of the carapace; preorbital segment with a short spine; arm nodular along dorsal margin; first, third, fifth and seventh branchial spines often larger than intervening spines. P. minor. (Fig. 36) (Common on the lower tidal of rocky and stony beaches; among weeds on piles; up to 1 ½ inches long.)
36(35) Rostral spines short, about 1/6th the length of the rest of the carapace; no spine on the preorbital segment. P. parvus. (Fig. 37) (Known from one small specimen, 1 cm. in length, taken from deep water.)

Key to the Species of Hymenosomidae

1 (2) External maxillipeds largely concealed beneath a wing-like plate; rostrum, simple, short, acute; carapace, circular, without mar-
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Figs. 39, Hombronia depressa; 40, Elamena longirostris; 41, E. producta (and leg); 42, Halicarcinus pubescens; 43, H. haasti; 44, H. lacustris; 45, Halicarcinus sp.; 46, H. cooki; 47, H. whitei (inset, rostrum); 48, H. planatus; 49, H. ovatus; 50, Ebalia cheesemani; 51, Petalomera lateralis. (Figs. 43, after Filhol; 44, after Chilton.)

Figs. 39, Hombronia depressa; 40, Elamena longirostris; 41, E. producta (and leg); 42, Halicarcinus pubescens; 43, H. haasti; 44, H. lacustris; 45, Halicarcinus sp.; 46, H. cooki; 47, H. whitei (inset, rostrum); 48, H. planatus; 49, H. ovatus; 50, Ebalia cheesemani; 51, Petalomera lateralis.
(Figs. 43, after Filhol; 44, after Chilton.)

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ginal teeth. Hombronia depressa. (Fig. 39) (Marine; probably among weeds; ½ inch.)
2 (1) External maxillipeds exposed, as is usual.
3 (8) Surface of carapace smooth, regions never delimited by sharp grooves; ischium of external maxillipeds longer than merus; maxillipeds completely closing buccal covern. G. Elamena.
4 (7) Rostrum projecting beyond the eyes.
5 (6) Rostrum narrow, produced; a strong spine extending from subrostral keel; carapace triangular; legs with many sturdy teeth. E. longirostris. (Fig. 40) (Offshore in deeper water; under ½ inch.)
6 (5) Rostrum produced, wide, obtuse; sub-rostral keel not spine-like; carapace, polygonal; distal end of merus of legs produced as an obtuse tooth, otherwise legs toothless. E. producta. (Fig. 41) (Symbiont in Haliotis; free-living offshore in deeper water; up to ½ inch.)
7 (4) Rostrum broad and obtuse not projecting beyond the eyes; carapace broader than long; no marginal spines. E. quoyi. (An inadequately described species.)
8 (3) Regions of carapace defined by sharp-cut grooves (which may show clearly only when dry); ischium of external maxillipeds not longer, frequently shorter than merus; the maxillipeds broad, and close or nearly closing buccal cavern; male abdomen with all sutures distinct; rostrum present. G. Halicarcinus.
9(16) Rostrum not strongly trilobate or tridentate, generally produced as a simple acute or obtuse triangle.
10(13) Posterior margin smoothly convex; margins toothless.
11(12) Rostrum an obtuse triangle; carapace sub-ovoid to ovoidal; everywhere hairy. H. pubescens. (Fig. 42) (Offshore in deeper water; ¼ inch.)
12(11) Rostrum triangular, sub-equilateral; antero-lateral margins straight, convergent, so that carapace widest posteriorly; not extensively hairy. H. haasti. (Fig. 43) (Unknown except for type.)
13(10) Posterior margin straight, at least never smoothly convex; marginal teeth generally present.
14(15) Carapace nearly circular, flat, with scattered hairs; two obscure teeth on antero-lateral margin; chelipeds and legs hairy; rostrum produced, concave above, distal end obtusely rounded. H. lacustris. (Fig. 44) (Freshwater, in lakes; small.)
15(14) Carapace ovoidal, dorsum hairless; anterior marginal tooth obsolete; posterior tooth acute, spine-like; rostrum variable, ranging from a broad obtusely rounded triangle to minutely tridentate as though eroded; in the male, digits of chela gaping proximally and dentate along distal half; palm with a dense
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patch of hair on medial surface. H. sp. (Fig. 45) (Possibly H. marmoratus Chilton; among weeds in tidal pools on mudflats, 1/3 inch.)
16 (9) Rostrum clearly trilobate or tridentate; never simply obtusely convex.
17(20) Rostrum produced as a platform above and beyond the eyes (as in Elamena), distally divided into lobes or teeth.
18(19) Anterior marginal tooth, rounded; posterior tooth submarginal, acute, spine-like; rostral lobes sub-equal; medial face of chela sparsely hairy; elsewhere hair scanty; digits of chela fully dentate and with full occlusion. H. cooki. (Fig. 46) (Among Zostera and other sea-weeds in pools on tidal mud-flats; 1/3 inch.)
19(18) No marginal spines or hooks; a prominent postocular tooth; median rostral tooth larger than laterals; chelipeds and elsewhere hairy. H. whitei. (Fig. 47) (As H. cooki, but also on piles of wharves; 1/3 inch.)
20(17) Rostrum represented only by three lobes or teeth, not produced as a platform; margin of carapace continues as a ridge across the front.
21(22) Marginal teeth absent or at best both obtuse; rostrum of three obtusely rounded low processes originating well below the rim of the carapace and with sub-parallel sides; in the male, the hand and fingers sturdy, the dorsal margin of the movable finger equals or barely exceeds the height of the palm. H. planatus. (Fig. 48) (Among weeds on piles, ships, etc., and in shallow sheltered water; ½ inch wide.)
22(21) Anterior tooth, obtuse, marginal; posterior tooth, acute, submarginal; rostrum of three acutely triangular teeth widely separated distally and arising barely below the margin; in the male, the hand long and tapering, the dorsal margin of movable finger exceeds height of palm. H ovatus. (Fig. 49) (Beneath stones at lower levels; up to ¾ inch wide.)

Key to the Species of Oxystomata

(Species recorded all belong to the F. Leucosiidae and to the genus Ebalia.)
1 (3) Carapace lacking prominent tubercles, finely granular.
2 (-) Posterior margin produced to give the appearance of three obtuse teeth; a single minute tooth at margin of branchial region. E. laevis. (Offshore; ½ inch long.)
3 (1) Carapace with large tubercles on dorsum; generally granular (but this feature highly variable).
4 (7) No lateral spine on the branchial margin.
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5 (6) Two tubercles on the cardiac region, one on each branchial in the male but these regions greatly swollen in the female; merus of cheliped, unarmed. E. tumefacta. (Reported from Cook Strait; a European species.)
6 (5) Tubercles arranged as a circle of five, with a sixth tubercle at the centre (the branchial tubercles may be nearly obsolete); two broad lobes on the posterior margin; merus of cheliped, unarmed. E. tuberculata. (An Australian species; offshore; ½ inch long.)
7 (4) Lateral spine on the branchial margin; posterior margin with an obtuse tooth at either end; a larger tooth above the middle and overhanging the posterior margin; the posterior margin of merus of cheliped with many small teeth. E. cheesemani. (Fig. 50) (Offshore; up to ¾ inch long.)

* Since going to press, a specimen of Latreillopsis petterdi trawled from Cook Strait has been shown me in the collection of the Dominion Museum. This means that both of the main subtribes of Dromiacea are represented here.