176 Dr. T. Wright on Fossil Echinoderms 



fasciole surrounds the ambulacral petals like an undulating 

 groove, as in Hemiaster, Schizaster, &c., it is said to be a peri- 

 petal ; when it surrounds the single ambulacrum, as in Amphi- 

 detuSj it is internal ; when it extends along the sides, as in Schi- 

 zaster, it is lateral ; when it surrounds the circumference of the 

 test, as in Pericosmus, it is marginal; when it is limited to the 

 base of the anal opening, it is subanal. We find sometimes in 

 the same genus more fascioles than one -, thus the subanal and 

 peripetal are frequently associated together. 



Genus Spatangus (Klein, 1734). 



Urchins, in general large with a thin test, a convex dorsal sur- 

 face, and the antero-lateral and postero-lateral ambulacral areas 

 composed of larger petals than in other Spatangidce. The ante- 

 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 Hqfmanni, Goldf. Petrefacta, Band i. p. 152. tab. 47. 



fig. 3a,b,c; Desmoulins, Etudes sur les Echinides, p. 398. no. 35 ; 



Grateloup, Mem. Echinid. Foss. tab. 1. fig. 8. p. 73 ; Agassiz 



and Desor, Ann. So. Nat. torn. viii. p. 7. 

 Echinus (petrefactus), Scilla, Corp. Mar. pi. 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- 



