296 Dr. T. Wright on the Cassidulidse of the Oolites. 



plate corresponds to a pair of pores, it follows that these are much 

 more closely set together on the dorsal than on the ventral sur- 

 face ; the interambulacral arese are very large ; the plates have a 

 crescentic form, the lower border being convex, and the upper 

 border more or less concave ; by reason of the great distance be- 

 tween the antero-lateral and postero-lateral ambulacra, the plates 

 forming the posterior pair of interambulacral areas are much 

 larger on the dorsal surface of the shell than their analogues of 

 the anterior iuterambulacra. The tubercles ai-e very uniformly 

 distributed upon the surface of the test, but are more numerous 

 upon the inferior than the superior surface. The epiderm which 

 covered the whole presented a finely granular aspect*. 



Affinities and differences. — This Urchin resembles D. ovalis, but 

 is distinguished from it by the unequal convexity of the dorsal 

 surface, the flatness of the base, and the greater proportional 

 distance between the points of convergence of the antero-lateral 

 and the postero-lateral ambulacra ; the form and structure of the 

 areae are likewise different ; in fact these characters form a good 

 diagnosis between D. analis and its congeners. Moreover D. 

 analis is found only in the Inferior Oolite, and D. ovalis is limited 

 to the Coralline Oolites. 



Locality and stratigraphical range. — The imperfect specimen 

 before me was obtained from the ferruginous beds of the Inferior 

 Oolite at Dundry ; it belongs to the Bristol Institution, and I 

 am indebted to the kindness of my friend Mr. Etheridge, the 

 Curator, for permission to describe the same. This species was 

 found by MM. Gressly, Hugi and Stromeyer in the Inferior 

 Oolite of Goldenthal and Fringeli (canton de Soleuref), and in 

 the Marn. vesul. (Inferior Oolite) of Wallenburg, Egg et Burg 

 (Afgovie), le Mont-Terrible, Saint Maixant, by Bronn, Thur- 

 mann and D'OrbignyJ. 



History. — Figured and described for the first time by Agassiz 

 in his ' Echinodermes Fossiles ' from specimens collected in the 

 Canton of Soleure, and subsequently by the authors cited in our 

 synonyma of this species, and now identified as a British Urchin 

 for the first time. D. analis must be rare, as the specimen be- 

 fore me is the only one I have met with in all the collections 

 I have examined with the view of ascertaining the species of 

 Echinoderms contained in our Oolitic system. 



* Echinodermes Foss. de la Suisse, 1st Part, p. 7- 



t Agass. Echinoderm. Foss. p. 6. 



X Annal. des Sciences Nat. torn. viii. p. 32. 



