The following key is designed for use by anyone without a specialised knowledge of echinoderms. Consequently the characters used are external ones, and the key is purely artificial. Only the shallow water species are included, except in the case of one or two species likely to be met with in fishermen's trawls down to 50 fathoms. None of the rarer forms are listed. The distribution is indicated in terms of the marine provinces, using the following abbreviations: A, Aupourian, i.e., the northern half of the North Auckland peninsula; C, Cookian, i.e., the remainder of the North Island, and the northern two-thirds of the South Island; M, Moriorian, i.e., the Chathams group; F. Forsterian, i.e., the southern third of the South Island, Foveaux Strait and Stewart Island; R. Rossian, i.e., the Auckland and Campbell Islands.

1.	Arms bordered above and below by a row of distinct marginal plates		3
2.	No marginal plates		13page 21
3.	Marginal plates of arms larger than those at the centre of the interadii		5
4.	Marginal plates largest at the interradius		7
5.	No more than four small marginal plates in each interradius and a pair of large swollen plates at each arm tip	CFM Pentagonaster pulchellus
6.	More than 15 marginal plates in each interradius, the penultimate plates near the arm-tip distinctly larger than those within or beyond.	C. Diplodontias dilatatus
7.	Outline more or less pentagonal, the arms not demarcated from the disc; marginal plates all approximately equal in size.	CFM Asterodon miliaris
8.	Arms 5, tapering evenly to the sharp tip, flattened above.		9
9.	Arms less than 8 cm. long		11
10.	Arms longer than 8 cm., usually 12 cm. or longer, both upper and lower rows of marginal plates covered with spines which overlap neighbouring plates.	C. Persephonaster neozelanicus
11.	Lower marginal plates provided with spines, upper marginals without them.	C. Psilaster acuminatus
12.	Both upper and lower marginal plates with spines.	AC Astropecten polyacanthus
13.	Arms distinctly separated from the small central disc region		19
14.	Arms broadening gradually towards the disc, and not distinctly demarcated		15
15.	Ambulacral groove narrow, slit-like		17
16.	Ambulacral groove half as broad as the arm.	FR Calvasterias suteri
17.	Outline pentagonal, without any interradial indentation. No trace of spines or spinelets above or below in life.	CM Stegnaster inflatus
18.	Outline roughly pentagonal, but usually with interradial indentation. Covered above and below with numerous clusters of minute spinelets.	ACFM Asterina regularis
19.	Arms 5 in number		21
20.	Arms 7-14 in number		23
21.	Arms bearing above 7 distinct longitudinal rows of spines.	CF Sclerasterias mollis

page 22 page 23

22.	Arms semi-cylindrical without distinct rows of spines, but with a granular coating.	CM Henricia compacta
23.	Arms and disc covered above by numerous small rounded pinhead granules. Arms 10-12.	ACMF Stichaster australis
24.	Arms and disc bearing prominent spines, each spine surrounded by clustered pedicellariae		25
25.	Spines bordering ambulacral groove longer than those of aboral surface. Arms 6-8, usually 7.	C Astrostole scabra
26.	Spines of aboral surface stouter than those bordering the ambulacral groove, and equal in length to the latter. Arms 6-11, usually 11, and commonly of unequal size owing to regeneration, of autotomised parts.	ACFM Coscinasterias calamaria

The four commonest starfish in Cook Strait rock-pools are: Asterina regularis, Stichaster australis, Astrostole scabra, and Coscinasterias calamaria.

Literature: This unfortunately is very scattered, but most important is Mortensen, Th. (1925), Vidensk. Medd. Dansk naturh. Foren., 79, p. 261, where further references will also be found. This publication is in the library of the Royal Society of New Zealand.

Explanation of Plate 2.

A, Asterodon miliaris, upper surface of one arm. B, Pentagonaster pulchellus, upper surface of one arm. C, Asterina regularis, lower surface of one arm. D, Sclerasterias mollis, cross-section of an arm, showing arrangement of spines. E, Stegnaster inflatus, lower surface of one arm. F, Stichaster australis, cross-section of an arm to show arrangement of granules and spines. G, Coscinasterias calamaria, crosssection of an arm to show spines. H, Astrostole scabra, cross-section of an arm to show spines. I, Psilaster acuminatus, side view of marginal plates of an arm showing arrangement of the spines on inferomarginal plates. J, Persephonaster neozelanicus, side view of marginal plates of an arm showing arrangement of spines on both superomarginal and inferomarginal plates. K, Diplodontias dilatatus, upper surface of an arm. L, Psilaster acuminatus, upper surface of one arm.