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



of the L. convexum has occurred, though unfortunately so col- 

 lapsed as not to exsert the organs, I have great hope this sum- 

 mer of meeting with it in a living state. 



I am, very faithfully, yours, 



William Clark. 



XXVI. — On the Cassidulidae of the Oolites, with descriptions of 

 some new species of that family. By Thomas Wright, M.D. 



&c. 



[Concluded from p. 214.] 



Dysaster analis, Agass. 



Syn. Dysaster analis, Agass. Prodrome Mem. Neuch. vol. i. 

 Collyrites analis, Desmoulins, Tab. Synop. p. 368. no. 14. 

 Dysaster analis, Agass. Echin. Suisse, i. p. 6. tab. 1. fig. 12-14; 



Gressly, Jur. Sol. p. 76 ; Desor, Monogr. des Dysaster, p. 10. 



tab. 2. fig. 8-10 ; Agassiz and Desor, Cat. raisonne des Echi- 



nides, p. 32. 



Test suborbicular, inclining to oval, more or less depressed, round 

 and inflated anteriorly, slightly contracted posteriorly ; dorsal 

 surface convex, more declined from the vertex to the anus than 

 from the vertex to the anterior border ; anterior half forming 

 the segment of a larger circle than the posterior half; vertex 

 excentral ; apical disc Dearly central, at which the single 

 ambulacrum and the antero-lateral ambulacra converge ; the 

 posterolateral ambulacra meet at the distance of y^ths of an 

 inch behind the anterolaterals ; anus nearly circular and pro- 

 minent, situated in the middle of the posterior border about 

 midway between the ambulacral arch and the basal angle ; 

 ventral surface flat, without undulations; mouth circular, 

 situated in a depression about the junction of the anterior 

 with the middle third of the ventral diameter ; sides convex, 

 suddenly declining from a slight median elevation. 



Height 1 inch, antero-posterior diameter 1 inch and y^ths, 

 transverse diameter 1 inch and y^ths. 



Description. — The nearly ovato-orbicular circumference and 

 depression of the dorsal surface, which is not uniformly convex, 

 with the flatness of the ventral surface, form a group of characters 

 by which this Dysaster is distinguished from its congeners. The 

 anterior half of the body is fuller and more developed, and forms 

 the segment of a larger circle than the posterior half. 



The single ambulacrum, which is lodged in a slight depression 

 on the anterior border, is wider than the others; the antero- 

 lateral ambulacra form graceful curves on the anterior sides of 



