220 



In the preceding genus, Perna, of Bruguiere, to which this genus 

 approaches the nearest, the hinge is also linear ; but it is formed of lonu 

 parallel grooves, which receive the ligament, and which have between 

 them parallel linear teeth, which shut against each other. But in Cre- 

 natula, the hinge shows a row of roundish or oval pits, by which it is 

 made to appear as if crenulated; and there are no linear teeth in the 

 interstices. 



Lamarck is acquainted with only two species of this genus : C. avicularis, 

 brought from the Antilles by Captain Baudin ; and C. mytiloides, which 

 is formed much like a mytilus y and which was found in the Red Sea. Ostrea 

 picta, Gmelin, he conceives, may perhaps be a variety pf this last shell. 



There are very few among the fossil shells of this, or of any other coun- 

 try, which, at first sight, are more dissimilar from any of the recent 

 shells, than the fossil represented Plate XV. Fig. 5. This fossil was 

 obtained by Mr. Strange, from Mr. Joshua Platt, of Oxford, who de- 

 scribed it on an accompanying ticket " Impression of an oyster, with 

 an indented cardo, out of a large nodule on the top of Shotover Hill." 



By some it has been considered as an Ostracite, by others as a Pernite ; 

 but neither by its general form, nor by any of its characters, could its 

 proper place be determined. The hinge had often been the subject of 

 my examination ; but the result was never any thing more, than that it 

 differed very materially from that of any genus with which I was ac- 

 quainted. The only information which any author yielded me respect- 

 ing it, was a very correct figure of a similar cast, by Lister, among the 

 fossil shells of that author, and marked as English, Hist. Conch. Tab. 477, 

 Fig. 34, b. 



A comparison of the hinge of this fossil with that which characterizes 

 this genus, immediately evinced their perfect agreement ; and showed 

 that two species are to be found, in very distant parts of the world, of 

 the same genus with this fossil, nothing analagous to which had been till 

 now discovered. 



