3i0 Dr. T. Wright on the Cassidulidse of the Oolites. 



which occupies the centre of the disc ; the five ocular plates are 

 small, and so firmly soldered to the ovarials that the line of the 

 sutures is entirely effaced. The base is flat and slightly undu- 

 lated, the interambulacral segments being moderately convex and 

 separated from each other by the straight, narrow ambulacra! 

 valleys. The mouth is nearly central, of a pentagonal form, and 

 surrounded by five prominent lobes formed of the terminal folds 

 of the interambulacra ; the tubercles on the dorsal surface are 

 very small and numerous, so that without the aid of a lens the 

 test appears smooth ; on the basal surface they are larger, but are 

 still comparatively small for so large an Urchin. 



Affinities and differences. — N. Agassizii resembles N. sinuatus 

 in size, but is readily distinguished from that common species by 

 the following diagnostic characters. In N. Agassizii the dorsal 

 surface is conoidal, the ambulacra are concave and depressed, the 

 anal opening is oblong and nearly superficial ; there is a consi- 

 derable extent of the test very slightly depressed between the 

 upper border of the opening and the disc, whilst in N. sinuatus 

 the anal valley extends from the disc to the border. The tubercles 

 are much smaller, and the dorsal surface is almost smooth. The 

 apical disc is large, superficial, and excentrical. 



Locality and stratigraphical rawye.— This Urchin was collected 

 from the sands of the Inferior Oolite in the neighbourhood of 

 Bridport. It occurs likewise near Ilminster in beds of the same 

 age. I know of no specimens in Gloucestershire. I dedicate this 

 species to Professor Agassiz, whose numerous monographs on the 

 Echinoderms, living and fossil, have so materially contributed 

 to advance our knowledge of this class. 



Nucleolites emarginatus, Forbes. 



Syn. Echinites suhulatuSy Young and Bird, Geol. Surv. York. Coast, 



p. 214.pl. 6. fig. 11. 

 Clypeus emarginatus, Phillips, Geol. of Yorksh. p. 127. pi. 3. fig. 18. 

 Nucleolites emarginatus, Forbes, Mem. of the Geol. Surv. Decade 1 , 



description of pi. 9. , 



''Test orbicular, sides declining, dorsal surface subdepressed; 

 vertex and apical disc nearly central : ambulacra broadly lan- 

 ceolate, with their apices approximated ; anal valley very short, 

 far removed from the vertex, obtuse and marginal ; posterior 

 lobes obsolete." — Forbes. 



Antero-posterior and transverse diameters about 4 inches. 

 We could not succeed in obtaining a specimen of this Nu- 

 cleolite ; it is said to be rare. Mr. Young observes, " that the 

 dorsal surface has the same elegant markings as No. 5 [Pygurus 

 pentagonalis), but the petals are rather oval shaped than lan- 

 ceolate, from which peculiarity we name it Echinites subulatus. 



