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. 1 52. tab. 4 7. 



fig. 3 a, 6, c\ Desmoulins, Etudes sur les Echiriides, p. 398. no. 35 ; 



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



and Desor, Ann. Sc. 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 T ^ inches, trans- 

 verse diameter 2 inches ; height anteriorly y^ths of an inch, 

 height posteriorly ^Jths 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 ; in this region the obsolete pores are clearly 

 seen : the antero-lateral ambulacral areas extend outwards at an 

 angle of 24 from a transverse lino drawn through the apical 



