Dr. T. Wright on the ( lauidulidtt of the Oolites. 181 



On the Ca8siduijd v. 



The Caasidulidse have been recently dismembered by Aga 

 and Desor from the family Clypeastrouhe, in consequence of the 

 mouth of the Cassidnlidse being destitute of the jaws and teeth 

 possessed by the true Clvpcastroidae* : how far this supposed ne- 

 gative edentulous character is of sufficient zoological importance 

 to justify the separation of the (assidulidse from the great natural 

 family which they resemble in most of the important points of 

 their structure, it is not our intention on the present occasion to 

 inquire ; it hat however the pabcontological merit of grouping 

 together many genera of Echinida closely related to each other 

 by structural affinities as well as by their limited distribution in 

 time. 



Family Cassidulidse. 



lii-bins having an oblong, subpentagonal or orbicular cir- 

 cumference, generally clypciform, with a uniform convex dorsal 

 surface, mostly depressed, but sometimes elevated or conoidal ; 

 the shell is of moderate thickness, and its surface is covered with 

 small tubercles and granules. The tubercles are smaller on the 

 dorsal than on the ventral surface, and are surrounded by a cir- 

 cular depression ; sometimes the tubercles are arranged in ver- 

 tical ranges, but in general they are sporadical. The granules 

 are entirely microscopic, and occupy the intertubercular spaces; 

 to the whole of the tubercles small filiform spines are attached. 

 The ambulacra] areae arc narrow, and the pores are disposed in 

 close-set pairs, forming a single file as in the Galerites ; or they 

 are placed at some distance apart, and united by transverse 

 sutures, which occasions the petaloid forms seen on the dorsal 

 surface of the test of the Nucleolites. 



The mouth is central or subcentral, and is sometimes armed 

 with jaws and teeth; in some genera its margin is divided into 

 ten lobes ; in others it is edentulous and the opening is round or 

 pentagonal, and sometimes surrounded by five prominent lobes, 

 formed by the folding inwards of the terminal portions of the 

 interambulacra. The anal opening is large, and situated on the 

 dorsal or ventral surface; it is rarely marginal, often infra-mar- 

 ginal, and when dorsal is lodged in a valley. The apical disc is 

 formed of four, perforated OVarial plates and a single imperforate 



* Thk generalization it not strictly in accordance with the facts. The | 

 ence <>t':i dental apparatus was discovered by Mr, ('has. Stokes in Ualerites 



alboi/a'rriK. | of this cretaceous I rchin. With the lantern ami 



teeth, are in the cabin >tokesand Bowerbank; [t is probable 



that all the members of the Qaleritc group with a central decagonal mouth- 

 opening possessed a similar dental armature. 



i "J 



