106 Dr. T. Wright on Fossil Echinoderms 



the anus, and meets the one from the opposite side, at the 

 middle line near the base ; in the triangle thus formed, the caudal 

 process and anus occupy the base, and a depression lies beneath 

 which is filled with tubercles somewhat larger than those 011 the 

 dorsum, but smaller than those on the base ; the tubercles are 

 perforated and raised on prominent crenulated bosses (fig. 3 c) ; 

 the sternal and basal portions of the test, as well as the anterior 

 border, being furnished with much larger tubercles. 



Affinities and differences. The straightness of the pairs of 

 ambulacra, and the narrowness of the single anterior ambulacrum, 

 are alone sufficient to distinguish S. Desori from S. aurynotus 

 when viewed only from above, but when we add to these the 

 remarkable oblique truncation of the posterior border (fig. 3 b), 

 the great tumidity of the sternum, and the sloping character of 

 the sides of the base, we discover how widely different these two 

 forms are from each other. The same group of characters serves 

 to distinguish it from S. Parkinsoni, but in this species the apical 

 disc is much nearer the centre of the test ; the antero-lateral 

 ambulacra are arched outwards, and the postero-laterals are pro- 

 portionately longer. 



Locality and stratigraphical position. Collected from the cal- 

 careous sandstone bed No. 4, at Malta ; the large specimen be- 

 longs to the Bristol Institution, the others form part of Earl 

 Ducie's collection. We dedicate this species to M. Desor of 

 Neufchatel, one of the learned authors of the 'Catalogue raisonne 

 des Echinides/ 



Schizaster Parkinsoni, Defrance sp. PL V. fig. 3 a-c. 



SYN. Spatangus Parkinsoni, Defrance, Diet. Sc. Nat. torn. 50. p. 96 ; 



Desmoulins, Etudes sur les Echinides, p. 394. no. 29. 

 Spatangus lacunosus, Parkinson, Organic Remains, vol. iii. tab. 3. 



fig. 12. 

 Schizaster Parkinsoni, Agassiz and Desor, Cat. raisonne', Ann. Sc. Nat. 



torn. viii. p. 22. 



Test cordate, depressed anteriorly, elevated posteriorly; apical 

 disc nearly central ; sides expanded and tumid ; cheeks sloping 

 and contracted ; single ambulacrum rather wider than the 

 anterior pair, of the same diameter throughout, except near 

 the apex; antero-lateral ambulacra diverge at an angle of 35; 

 length 1 inch ; postero-lateral make an angle of 65 ; length 

 T %ths of an inch ; posterior part of the back raised into a long 

 prominent carina ; posterior border obliquely truncated ; base 

 convex ; mouth near the anterior border ; antcal sulcus nar- 

 row and of moderate depth. 



Dimensions. Adult. Antero-posterior diameter 2^J inches, 

 transverse diameter 2^ inches, height 1J inch. 



