36 
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 spies; 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. 
Il. Tubercles imperforated. 
Echinide, Gray, 1828. 
Fam. 3. ARBACIAD. 
Ambulacral area narrow; ambulacra narrow, with a single series 
of double pores ; body circular ; spines short, solid. 
1. Agarites. Upper surface of the interambulacral area without 
tubercles. 
2. Arbacia. The upper and lower surface of the interambulacral 
area covered with tubercles. 
Fam. 4. Hipronoip2. 
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. Hipponoé (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- 
simus. 
Fam. 5. Ecuinip#. 
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. 
A. With angular pores at the junction of the plates. 
1. Mespilia. 2. Microcyphus. 3. Salmacis. 4. Temnopleurus. 
B. Without any pores at the angles of the plates. 
5. Echinus. 6. Psammechinus. 7. Heliocidaris. 
