280 Zoological Society : — 



1. Cidaris. Tessera even-topped. 



2. Goniocidaris. Tessera bevelled on the edge. — G. 2)istilliiris. 



Fam. 2. Diademad^. 

 Ambulacra narrow, of one series of double pores ; intorambulacral 

 plates numerous, with two or more rows of tubercles ; spines slender, 

 often tubular. 



1. Astropy(ja, Body depressed ; ambulacral area with very small 

 crowded tubercles, bearing very thin spines, much smaller than the 

 interambulacral spines and tubercles ; interambulacral area with 

 smooth bands. 



2. GareJia. Body depressed ; ambulacral area narrow, with two 

 or four series of small tubercles, and thin spines ; interambulacral 

 area with oblique series of large tubercles and spines, but without 

 any smooth band ; spines tubular. 



3. Biadema. Body globular or subdepressed ; ambulacral area 

 with the same sized tubercles and spines as the interambulacral area. 



II. Tubercles imperforated. 

 EchinidcB, Gray, 1828. 



Fam. 3. Arbaciad^. 



Ambulacral area narrow ; ambulacra narrow, with a single series 

 of double pores ; body circular ; spines short, solid. 



1 . Jgarites. Upper surface of the interambulacral area without 

 tubercles. 



2. Arbacia. The upper and lower surface of the interambulacral 

 area covered with tubercles. 



Fam. 4. Hipponoid^e. 



Ambulacral area as wide as the interambulacral ; ambulacra wide, 

 formed of three separate vertical rows of double pores. Body cir- 

 cular ; shell thin. 



1. Amblypneustes. Body high ; porous zones not quite regular; 

 mouth small, entire. — A. ovvm. 



2. Boletia. Body depressed ; porous zones regular, inner sepa- 

 rated by a vertical series of tubercles ; mouth very large, with five 

 deep slits. — B. pileolus. 



3. Hippono'e (Gray, 1841). Body swollen; two outer porous 

 zones regular ; middle one interrupted ; mouth small, slightly cut. — 

 //. Sardiccf. 



4. Holopneustes. Body swollen ; two outer porous zones regular ; 

 middle one separate or interrupted ; mouth small, entire. — //. poris- 

 simus. 



Fam. 5. Echinid^. 

 Ambulacral area lialf as wide as the interambulacral area, with 

 two (or three) close series of double pores, placed in threes ; buccal 

 membrane naked ; body circular. 



