BRITISH. FOSSILS. 



DscADS V. Plate YIII. 



PYGASTSil C0N0IDEU3. 



[Genus PYG ASTER. Agassiz (1834.) (Sub-kingdom Radiata. Class Ecliinoder- 

 mata. Order Echinoidea. Family Cassidulidse.) Orbicular, depressed or sub -conic ; 

 ambulacra simple throughout ; tubercles perforate (and crenulate ?), disposed in Yery 

 regular series in both areas ; anus very large, superior, generally placed near the plates 

 of the disk ; mouth decagonal, no tubercles round it.] 



Diagnosis. P. pyrmnidalis peiitaedrus, margini postico siihacuto ; tuber- 

 cults minutis et ut sparsis, suhtus majoribus et crebris; ambulacris elevatisy 

 angustis : ano modico, nec dimidium inter ambulacri planati efficiente. 



Sywonois. Pyg aster conoideus, Wright, Ann. and Mag. Nat. Hist. 

 (1852), vol. ix. p. 91. pi. 3. %. 1. 



The only cabinet that appears to contain this well-marked species 

 is that of our friend Dr. Wright, who has lent it us for figuring. 

 We may expect soon a full account from him, and of other British 

 species not here mentioned, in the volumes of the Palgeontographical 

 Society. 



It is more conoidal than any of its genus, the anterior and lateral 

 surfaces forming angles of from 50° to 55° with the base, and the 

 posterior side an angle of about 42°. Its height is an inch and 

 and its diameter nearly 2 J inches either way (Wright). The base 

 is nearly flat so far as it can be seen. The ambulacra are narrow 

 and prominent, and are placed at equal distances, each being less 

 than one fourth the width of the intervening spaces. The three 

 anterior radiate in straight lines from the depressed disk, which is 

 lost in our specimen ; the two posterior curve first outwards to 

 avoid the edges of the anal opening, and then proceed straight to 

 the margin. 



[V. viii.] 5 H 



