16 



" The mouth is centrai. The vent none. 



" The cavity is simple. 



" Tlie parietės are thin and minutely dotted, and the centre of 

 the dorsal disc is pellucid. 



" This genus is very nearly allied to the fossil described by Dr. 

 Goldfuss in his beautiful \vork on Petrifactions, under the name of 

 Glenotremites paradoxus (tab. 4'9. f. 9. and t. 51. f. 1.), with which it 

 agrees in external appearance and form, in the possession of 

 a sunken space on its upper surface, and in liaving only a single in- 

 ferior pentagonal mouth. It difFers from Glenotremites by beingun- 

 furnished with ambutacra running from the angle of the mouth to 

 the margin, by being unprovided with conical cavities between those 

 near the mouth, and by having in the flattened disc on the back a 

 centrai ąuadrangular impression instead of the pentagonal star of 

 that genus. 



*' Dr. Goldfuss describes the glenoid cavities on the surface as 

 giving attachment to spines simiiar to those of the Turhan Echini, 

 (Ct«/am,Lam.),and statės that the under surface is covered with very 

 small tubercles to which he believes spines were attached. The 

 cavities on the surface of Ganymeda and the pits in them have very 

 much the form of those figured by Dr. Goldfuss in his fossil, but 1 

 cannot regard them as being fitted for the attachment of spines : 

 they have much more resemblance to the mouths of cells. Sogreat, 

 indeed, is this resemblance, that I entertained doubts vvhether the 

 whole mass might not be a congeries of cells likę the Lunulites, 

 rather than the case of a single body, until I considered that it was 

 impossible, from its form, that it could increase in size with the 

 growth of the animal, and that its exceeding regularity proved that 

 it mušt be the formation of a single creature. 



" I am induced to consider these two genera, though differing in 

 the above-stated particulars, as forming a family or order between 

 the Echinida and the Asteriidce; allied to the latter in having only 

 a single opening to the digestive canal,and agreeing vvith the former 

 in form and consistence, but differing from it in not being composed 

 of many platės. 



"I only know t\vo specimens of this genus, which I believe were 



found on the coast of Kent, as I discovered them mixed with a quan- 



tity of Discopora Patina which I coUected several years ago from 



Jiici and shells on that coast. The specimens are -^ of an inch in 



diameter. 



" I propose to call the species Ganymeda pulchella." 



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