264 Dr. T. Wright on Fossil Echinoderms 



the following characters : — S. eurynotus is broader and more 

 depressed before, and is not proportionally so high behind as 

 S. canaliferus ; the antero-lateral ambulacra are more divergent, 

 and the postero-lateral pair are proportionally longer in *S^. eury- 

 notus than in S. canaliferus. The single ambulacrum is about 

 the same depth as the pairs, and has the pores in a single file in 

 S. eurynotiis, whereas in S. canaliferus this area is much deej)er, 

 and the ])ores are not in single filr, but are crowded together, so 

 that they foi'm three rows in a part of the zone ; the tubercles 

 of the base are much larger in the living than in the fossil 

 species. ^9. eurynotus is distinguished from >S^. Parkinsoni by 

 its y-shaped ambulacra being less divergent, and the position of 

 the apical disc, which is much nearer the posterior border in ^S^. 

 eurynotus ; the anterior ambulacrum is likewise much wider and 

 deeper in that Urchin than in S. Parhinsoni : the great develop- 

 ment of the single interambulacrum, and breadth of the pos- 

 terior border in S. Desori s\:fficiently mark that species as 

 widely distinct from S. eiirynotus. 



Locality and position. — Collected in bed No. 4, the calcareous 

 sandstone at Malta ; we have it also from Santa Manza, Corsica, 

 sent us by M. Michelin ; it has likewise been found in the Ter. 

 moyen dc Perpignan, Cagliari. 



Schizaster Desori, Wright, n, sj). PI. VI. fig. 3 a-c. 



Test cordate, broad and ■ much depressed before, narrow and 

 much elevated behind ; ambulacral areas long, straight, and 

 very divergent; peripetal fasciole forms an acute angle on the 

 anterior interambulacra ; apical disc situated at the posterior 

 third of the dorsum ; angle of the antero-lateral ambulacra 

 44^ ; angle of the postero-lateral pair 60° ; posterior border 

 truncated obliquely downwards and inwards ; sternal portion 

 of the interambulacrum tumid and prominent at the base, 

 amounting almost to a deformity. 



Dimensions. — Antero-posterior diameter 2 ^-^ inches, transverse 

 diameter 2^-^ inches, height at the deepest part ly^^ inch. 



Description. — This remarkable Urchin wants the symmetrical 

 proportions of the other Schizasters met with in the same rocks ; 

 it is rounded and broad before, and tapers into a narrow wedge- 

 shape process behind ; the dorsal surface inclines forwards at an 

 angle of 17°; the ambulacral areas are long. The single anterior 

 area compared with S. eurynotus is narrow, and of a uniform 

 width ; it is l/j5 inch in length from the apical disc to the 

 fasciole ; there are twenty-four pairs of pores in the avenues, 

 the external being much larger than tlie mternal row, although 

 this is properly speaking a generic chaiacter. The antero-lateral 



