104 Dr. T. Wright on Fossil Echinoderms 



basal portions of the lateral and anterior pairs slope gently 

 towards it ; the tracks of the ambulacra are nearly naked as they 

 approach the mouth, and are here perforated with buccal pores. 

 The mouth is at the anterior third, and has a projecting under- 

 lip; the tubercles on the upper surface are small and of a 

 uniform size ; those on the sternum are larger, and are per- 

 forated and set on crenulated summits ; they are arranged in 

 lines radiating from a posteal point ; the tubercles of the inter- 

 ambulacral pairs are the largest. 



Affinities and differences. This species very much resembles 

 the living S. canaliferus, but it may be distinguished from it by 

 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. eurynotus, whereas in S. canaliferus this area is much deeper, 

 and the pores are not in single file, but are crowded together, so 

 that they form three rows in a part of the zone ; the tubercles 

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

 species. S. eurynotus is distinguished from S. Parkinsoni by 

 its /-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. Parkinsoni : the great develop- 

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

 terior border in S. Desori sufficiently mark that species as 

 widely distinct from S. eurynotus. 



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. 

 tnoyen de Perpignan, Cagliari. 



Schizaster Desori, Wright, n. sp. 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 fascicle 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 f 8 ^ inches, transverse 

 diameter 2 T 7 ^ inches, height at the deepest part 1 T % inch. 



