Tentacle-pores large and conspicuous.

Radial shields large. Lateral plates carrying a row of ca. 5 spines, and also a parallel row of ca. 5 hyaline hooklets: dorsal interradii deeply furrowed. . . . Ophiodictys Koehler, 1922a.

Syn.: Ophiodaces Koehler, 1922.

*inanis Koehler, 1922a. Antarctic. 120 fms.

Radial shields small or lacking.

Disc covered by naked skin or fine scales.

Disc higher than wide, arms capable of standing vertically over the disc, page 16and assuming this position in preserved material: several rows of flat oral papillae.

This assemblage includes Ophiotholia and Ophiomyces, which Verrill (1899) treated as a distinct family, the Ophiomycetidae; of subsequent writers, Koehler alone adopts Verrill's proposed family. Fell (1941) described a similar arm-posture in juvenile stages of "Kirk's ophiuroid", a species which is now believed to be referable to Ophiomyxa. If Verrill's Ophiomycetidae is valid, it would also include Ophiothauma H. L. Clark, 1938.

Seven arms. . . . Ophiothauma H. L. Clark, 1938.

*heptactis H. L. Clark, 1938. N. Australia. Littoral.

Five arms.

About 3 arm-spines, plus, on the distal arm-segments, some hyaline umbrella-shaped hooklets. . . . Ophiotholia Lyman, 1880.

*supplicans Lym., 1880. Juan Fernandez. 1,800 fms.

About 10–12 arm-spines: no accessory hooklets. . . . Ophiomyces Lyman, 1869

*frutectosus Lym., 1869. N. Atlantic. 100 fms.

Disc not high: arms normal.

Disc covered by naked skin, not containing plates: 6 or 7 flat, pointed, hyaline arm-spines. . . . Ophioblenna Lütken, 1959.

*antillensis Lütk., 1859. West Indies. Littoral.

Disc covered by scales above and below, or by thick skin in which embedded plates are visible when dried.

Disc completely scaled above and below.

No evident genital clefts, the disc continuing unbroken across the dorsal surface of arms: no evident radial shields: no tentacle-scales. . . . Ophiocymbium Lyman, 1880.

*cavernosum Lym., 1880. Kerguelen. 2,000 fms.

Genital clefts in usual position: tentacle-scales spiniform

Evident radial shields. . . . Amphipsila Verrill, 1899.

H. L. Clark (1915) refers this sp. to Ophiopsila.

*maculata Verrill, 1899. Caribbean. 200 fms.

Radial shields not evident.

Oral papillae scale-like. . . . Ophiologimus H. L. Clark, 1911.

*hexactis H. L. C., 1911. Japan. 100 fms.

Oral papillae of 2 types: the inner ones scale-like, the outer ones elongate and spiniform. . . . Ophiophrura H. L. Clark, 1911.

Koehler (1922) points out that Ophiophrura is closely comparable with Ophiomedea, and could well be included in the latter: they are kept separate here because of the practical convenience of using the disc-clothing as a key-character.

*liodisca H. L. C., 1911. Japan. 500 fms.

Disc covered by a rather thick skin, which contains embedded plates, visible when dried.

Embedded disc-plates imbricating: oral papillae all spiniform: four or five slender, cylindrical tapering smooth arm-spines: tentacle-pores large, 1 small tentacle scale at base of arm, none thereafter. . . . Ophiotoma Lyman, 1883.

Syn.: Ophiopora Verrill, 1899.

*coriacea Lym., 1883. North Atlantic. 1,200 fms.

The soft thick skin of the disc contains rounded small plates which do not imbricate, and small radial shields: internal oral papillae spiniform, page 17external ones flat and spatulate. . . . Ophiosparte Koehler, 1922.

*gigas Koehler, 1922. Antarctic Ocean. 100 fms.

Disc bearing granules or spines.

Dorsal arm-plates visible, not obscured by granules or spinules.

Tentacle scales elongate, spiniform.

Arms barely twice as long as disc-diameter, broad at the base and tapering rapidly: radial shields visible: each disc scale carrying a trifid stumpy spine: 1 tentacle-scale. . . . Ophiodelas Koehler, 1931.

*insignis Koehler, 1931. Indonesia. 150 fms.

Arms many times longer than disc diameter: radial shields mainly or completely concealed.

Eight or 9 spiniform oral papillae which are confluent with 6 or so papillae of the oral tentacle pore: 3 or 4 small spiniform tentacle-scales. . . . Ophiotrema Koehler, 1896.

*alberti Koehler, 1896. Azores.

Three or 4 oral papillae confluent with 3 or 4 larger and flatter papillae of the oral tentacle pore: 2 or 3 spiniform tentacle-scales. . . . Ophioprium H. L. Clark, 1915.

*Ophiacantha cervicornis Lym., 1883. Atlantic O. 500 fms.

Tentacle scales 2, flattened, oval; outer oral papillae elongate, spiniform. Ophiomedea Koehler, 1906.

Compare also Ophiophrura, paragraph No. 17 above.

*duplicata Koeh., 1906. N. Atlantic. 1,100 fms.

Dorsal surface of disc and arms so thickly covered with granules and spinules as to hide the dorsal arm-plates and radial shields: several spiniform, tentacle-scales. . . . Ophiambix Lyman, 1880.

*aculeatus Lym., 1880. Fiji. 1,300 fms.

Tentacle-pores small and inconspicuous.

Radial shields small and short.

No genital plates or scales: an accessory perforated plate between the oral shield and the peristomial plate. . . . Microphiura Mortensen, 1911.

*decipiens Mort., 1911. West Indies. 500 fms.

Genital plates present: oral plates without accessory plate.

Oral shield separated from the first lateral arm-plate by adoral shield.

Disc scales almost naked. . . . Ophiocopa Lyman, 1883.

*spatula Lyman, 1883. Indian Ocean. 150 fms.

Disc scales bearing spines on granules.

Outermost oral papillae large and operculiform. . . . Ophiolimna Verrill, 1899.

*Ophiacantha bairdi Lyman, 1883. North Circumpolar. 500–1,400 fms.

Ophiolimna is not recognized by H. L. Clark (1915).

Oral papillae all similar, none operculiform. . . . Ophiomelina Koehler, 1922a.

*Ophiomitrella placida Koehler, 1904. Indonesia. 400 fms.

H. L. Clark (1915) referred the type to Ophiacantha.

Oral shields adjoin first lateral arm-plate.

Dorsal arm-plates small, widely separated by the lateral plates which meet on the midline. Disc covered above by large plates which are closely granulated save at their margins, which are hyaline. . . . Ophioripa Koehler, 1922a.

*marginata K., 1922a. N. Pacific. 500 fms.

Compare also Ophiomitrella (No. 61a of this key).

Dorsal arm-plates in contact on basal segments, at least, and elsewhere not widely separated by lateral plates.

Basal tentacle-pores greatly enlarged: no tentacle-scale. . . . Ophientrema Verrill, 1899.

*Ophiacantha scolopendrica Lyman, 1883. Japan. 600 fms.

Basal tentacle-pores not enlarged: oval radial shields.

Ventral arm-plates visible: single flat tentacle scale. . . . Ophiophthalmus Matsumoto, 1917.

Syn. Ophiosemnotes Matsumoto, 1917.

*Ophiacantha cataleimmoida H. L. C., 1911. N. Pacific. 300–500 fms.

Ventral arm-plates obscured by thick skin: 2 tentacle-scales. . . . Ophiochondrella Verrill, 1899.

*Ophiochondrus squamosus Lyman, 1883. St. Kitts. 250 fms.

Referred by H. L. Clark (1915) to Fam. Hemieuryalidae.

Radial shields large.

Radial shields long and narrow.

Radial shields joined in pairs. . . . Ophiacanthella Verrill, 1899.

*Ophiacantha troscheli Lyman, 1878. Atlantic. 100 fms.

Radial shields separated.

Distal borders of dorsal arm-plates bearing each a row of spines. . . . Ophiogema Koehler, 1922a.

*punctata Koehler, 1922a. Indonesia. 100 fms.

Dorsal arm-plates without spines.

Disc scales not covered by skin: dorsal arm-plates mostly in contact: 1 large tentacle scale. . . . Ophialcaea Verrill, 1899.

*Ophiacantha tuberculosa Lyman, 1878. Philippine Is. 400 fms.

Disc and arms covered by skin.

Disc covered by thin skin bearing granules and stumps: the underlying scales can be seen when dried: arm-spines hollow. . . . Ophiacantha Mueller & Troschel, 1842. Syn. Ophiotreta, Verrill, 1899a; Ophiectodia Verrill, 1899a: Ophientodia Verrill, 1899a: Ophiodiplax Koehler, 1911 = Ophioscalus Verrill, 1899a; Ophiopristis Verrill, 1899a. See Disc. Rpts., Mrtsn. (1936).

*Asterias bidentata Retzius, 1805. N. Atlantic. Littoral. 1,300 fms.

Enlarged operculiform outer oral papillae and adoral plates with an enlarged distal lobe are characters which occur in Ophiotreta Verrill (type Ophiacantha lineolata Lyman, 1883, Caribbean, 200 fms.). Ophiotreta is recognised as a valid genus by Koehler and by H. L. Clark (who synonymizes Ophiurochaeta Matsumoto with it).

Disc covered by thick skin, bearing granules and stumps: arm-spines short, blunt, and invested in thick skin. . . . Ophiolebes Lyman, 1878.

*scorteus Lym., 1878. Antarctica. 300 fms.

Radial shields broad: disc plates very distinct, not hidden by skin.

Oral papillae arranged in a regular series.

Outermost oral papilla large and operculiform: dorsal arm-plates small, widely separated from each other by lateral plates.

Disc five-lobed, radial shields contiguous, at least distally: oral shield small, and separated from first lateral arm-plate by adoral shield: jaws somewhat sunken, so that the oral and adoral shields form a conspicuous elevated page 19ring: no genital plates. . . . Ophiothamnus Lyman, 1869.

Syn. Ophioleda Koehler, 1906, according to Matsumoto (1917).

*vicarius Lyman, 1869. Caribbean. 20 fms.

Disc not five-lobed: radial shields contiguous along most of their length: oral shield large, adjoining lateral plate: genital bursae well developed. . . . Ophiurothamnus Matsumoto, 1917.

*Ophiomitra dicycla H. L. C., 1911. N. Pacific. 400 fms.

Outermost oral papilla not enlarged.

Disc not five-lobed—i.e., lacking a notch in the edge of each interradius. Disc set with short stumps or glassy granules which do not conceal the scales. 1 tentacle-scale. Dorsal arm-plates not contiguous. . . . Ophiomitrella Verrill, 1899.

*Ophiacantha laevipellis Lyman, 1883. Caribbean. 100 fms.

Disc five-lobed, having deep interradial notches in its edge. Dorsal arm-plates contiguous.

Marginal disc-scales differentiated and well developed. . . . Ophioplinthaca Verrill, 1899b.

*Ophiomitra dipsacos Lym., 1878. West Indies. 400 fms.

Marginal scales not specially developed: disc scales very robust, comprising mainly radial shields plus some intercalary plates. . . . Ophiomytis Koehler, 1904.

*weberi Koehler, 1904. Indonesia. 300 fms.

Oral papillae not in a single series, but forming clusters at the ends of the oral angles. Disc more or less five-lobed.

Marginal disc-scales differentiated and well developed: radial shields not in contact: 1 tentacle-scale. . . . Ophiomitra Lyman, 1869.

Lyman specifically cites the large broad radial shields as characteristic of his genus (see also Lyman, 1882, p. 202). Mortensen (1933, p. 42) refers his species hamula to Ophiomitra, although the radial shields are "rather small". It seems doubtful whether hamula, as also O. spinea Verrill, really belong in Ophiomitra, but I have no material on which to base a conclusion.

*valida Lyman, 1869. Caribbean. 120 fms.

Marginal scales not specially differentiated: radial shields contiguous along their whole length: 3 tentacle-scales, shaping a ring about the pore. . . . Ophiocamax Lyman, 1878.

*vitrea Lyman, 1878. Indian O. 150 fms.