82 Dr. T. Wright on Fossil Echinoderms 
rior ambulacrum is lodged in a deep anteal sulcus; the upper 
part of the anterior border of the antero-laterals is obliterated 
towards the summit. 
Numerous very large crenulated and perforated tubercles are 
scattered over the surface of the ambulacral plates. They have 
a deeply grooved subanal fasciole; only four genital pores, the 
anterior pair more closely approached than the posterior pair. 
Five perforated ocular plates, arranged in the form of a pen- 
tagon, around the genital pores. A tube or hollow cone at the 
internal part of the single interambulacrum. A large vertical 
plate passing into a cone arises from the internal surface of the 
test upon the left side of the mouth, and is directed obliquely 
upwards and backwards. 
The species are living or fossil in the tertiary rocks. 
Spatangus Hoffmanni, Goldfuss. 
Syn. Spatangus Hoffmanni, Goldf. Petrefacta, Band i. p. 152. tab.47. 
fig. 3 a,b,c; Desmoulins, Etudes sur les Echinides, p. 398. no.35; 
Grateloup, Mém. Echinid. Foss. tab. 1. fig. 8. p. 73; Agassiz 
and Desor, Ann. Sc. Nat. tom. vii. p. 7. 
Echinus ( petrefactus), Scilla, Corp. Mar. pl. 10. fig. 1. 
Test convex, depressed anteriorly, elevated and carinated 
posteriorly ; antero-lateral and postero-lateral interambulacra 
with numerous large, perforated and crenulated tubercles, 
surrounded by deep sunken areolas ; base convex, the postero- 
lateral areas with large tubercles ; interambulacrum forming 
a tumid projection at the base; mouth and anus large; mar- 
ginal fold acute ; the pores in the zones large, disposed in 
wide-set pairs. 
Dimensions. — Antero-posterior diameter 2%, inches, trans- 
verse diameter 2 inches; height anteriorly ;4ths of an inch, 
height posteriorly }4ths of an inch. 
Description.—The characters of this form of Spatangus are so 
prominent and well defined, that one is astonished that between the 
time of Scilla, who first figured it, and that of Goldfuss, who first 
described it, no zoophytologist should have become its historian. 
The dorsal surface of the test is broad, convex, and depressed 
anteriorly, and narrow, elevated, and carinated posteriorly ; the 
ambulacral areas are well defined, the single ambulacrum with 
its rudimentary pores is lodged in a wide but shallow anteal 
sulcus, and there is a flattened plateau between the sulcus and 
the apical disc; m this region the obsolete pores are clearly 
seen: the antero-lateral ambulacral areas extend outwards at an 
angle of 24° from a transverse line drawn through the apical 
