280 Zoological Society : — 



1. Cidaris. Tessera even-topped. 



2. Goniocidaris. Tessera bevelled on the edge. — G. pistillaris. 



Fam. 2. Diademad^e. 



Ambulacra narrow, of one series of double pores ; interambulacral 

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

 often tubular. 



1. Astropyga. 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. Garelia. 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. Diadema. 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. HipPONOiDiE. 



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. ovum. 



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. Hipponoe (Gray, 1841). Body swollen; two outer porous 

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

 H. Sardica. 



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

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

 simics. 



Fam. .5. Echinid^. 

 Ambulacral area half as wide as the interambulacral area, with 

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

 membrane naked ; body circular. 



