26G Dr. T. Wright on Fossil Echinoderms 



are alone sufficient to distinguish S. Desori from *S^. euryjiotus 

 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. 



Loculity 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 raiscnne 

 des Echinides.^ 



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



Syn. Sjpatangus Parkinsoni, Defrance, Diet. Sc. Nat. torn. 50. p. 96 ; 



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

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



fig. 12. 

 Schizaster Parkinsoni, Agassiz and Desor, (^at. raiscnne, Ann. Sc. Nat. 



tom. 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-latcral make an angle of 65°; length 

 j^^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 ; anteal sulcus nar- 

 row and of moderate depth. 



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

 transverse diameter 2^-^- inches, height 1^^ inch. 



Junior. Antero-posterior diameter 2 inches, transverse dia- 

 meter ly^^j inch, height ly^^ i"*^^- 



Description.— We have identified this Urchin with that figured 

 by Parkinson in his ' Organic Pteniains,' not however without 

 much hesitation, inasmuch as that figure is without details, and 

 is moreover drawn from a distorted specimen. We have in vain 

 endeavoured to find out the original, and have therefore, from 

 the centi'al position of the apical disc and the great divergence 

 of the ambulacra, and from its being at the same time the most 



