20 1 Dr. T. Wright on the Cassidulidie of the Oolites. 



pores are small and distinct, and more numerous in the avenues 

 than in the preceding species ; the apical disc is formed of four 

 ovarial plates and three large ocular plates, the mode of arrange- 

 ment appearing to resemble that described in D. ringens, but we 

 cannot state precisely their structure from the condition of the 

 test. 



M. Cotteau observes that D. ovalis has been collected in the 

 two divisions of the Oxfordian stage (departement de PYonne), 

 and in each it presents a distinct variety. In the ferruginous 

 beds which repose upon the upper layers of the Bathonian stage 

 it is of small size, and is flattened before, contracted behind, and 

 almost flat above ; in the Oxfordian limestones or upper division 

 of this stage it is much larger in size, of a regular oval form, 

 with more tumid sides : both of these varieties are figured in his 

 work *. 



Affinities and differences. — Adopting as we do the careful ob- 

 servations made by Agassiz and Desor on this species, who regard 

 D. propinquus and D. truncatus as varieties of D. ovalis, these 

 forms are readily distinguished from their congeners by the 

 uniformly tumid oval form of the test. The large variety of 

 D. ovalis however much resembles D. analis, but the former is 

 distinguished from the latter species by the structure of the am- 

 bulacra ; in D. analis the postero-lateral arese converge imme- 

 diately above the anal opening, whilst in D. ovalis their point of 

 convergence is at some distance before that opening. 



Locality and stratigraphical range. — This species was obtained 

 by the Rev. Mr. Young f and by Mr. Phillips % from the calca- 

 reous grit, and by the latter from the Coralline Oolite and Kel- 

 loway rock of Yorkshire. Its foreign distribution, according to 

 Agassiz and Desor's Catalogue §, is from the " Argovien du Frin- 

 geli, Liesberg, Largue, Walen, D'Elemont, Purrentruy, Palins, 

 Mont Bregille, near Besancon." It has been collected from the 

 two divisions of the Oxfordian stage by M. Rashier, from the fer- 

 ruginous beds at Gigny, and from the calcareous beds at Villiers- 

 les-Hauts, departement de PYonne||. 



History. — Our table of synonyms, to which we refer, gives the 

 history of this species; it has been figured as a British Urchin 

 by Parkinson, Young and Bird, and Phillips, in their respective 

 works, but in all so badly that their figures are worthless ; Agassiz 



* Ktudes des Echiuides, p. 87. 



t Geological Survey of the Yorkshire Coast, p. 21.5. 



X Geology of Yorkshire, p. 134. 



§ AnnaK's des Sciences Naturelles, torn. viii. p. 32. 



I| Cotteau, Benin, loss. p. &7. 



