OF NEW SOUTH WALES. 157 



This genus is well represented in Australia, and generally goes 

 by the name of Gidaris. It lives in the hollows of rocks, browsing 

 on seaweed, and is often left by the tide at low water. The 

 spines are exceedingly sharp, and inflict painful wounds when 

 carelessly handled. We have three species in Australia. 



Strongylocentrotus armiger, A. Ag. 



Test thin, flattened above, regularly arched below. Is at once 

 distinguished from its congeners by its short, thick, swollen 

 spines. Largest primary tubercles of both areas within three 

 plates of abactinal system in the I. space. They cover the abac- 

 tinal part of the flattened test, decreasing rapidly towards the 

 ambitus and actinal surface. I have not seen this species, and 

 do not know in what part of Australia it occurs. 



Strongylocentrotus eurythrogrammus, Valenciennes. 



The commonest of our species. Easily distinguished by its 

 olive brown spines, though there are white varieties in Tasmania. 

 Test regularly arched, subglobular or depressed. Two principle 

 vertical rows of tubercles in the A. and I. space, a well defined 

 vertical row of small tubercles separating the porif. zones from 

 the primary tubercles in the I. space. Two irregular medium 

 vertical interambulacral rows. Coronal plates closely crowded 

 with small secondaries ; the intervening space again crowded 

 with closely packed milliaries surrounding them. Porif. zone 

 broad, pores arranged in oblique arcs, separated by irregular 

 rows of secondaries. Cuts very moderate. Membrane thin, with 

 a few elliptical plates. 



Found at low water in all B. Australia, as far as Cape York ; 

 Southern Australia, Bass Straits and Tasmania. 



Strongylocentrotus tuberculatus, Lamarck. 



Test greenish, spines large, sharp, and long, in colour, dark 

 violet, or black. Anal system elliptical, covered by small plates, 

 carrying a few minute tubercles. Madreporic body large and 

 pentagonal. Two main rows of tubercles in the A. and I. spaces, 

 each flanked in the I. space by a smaller one, meeting in a single 



