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 
long parallel grooves, which receive the ligament, and which have 
between them parallel linear teeth, which shut against each other. 
But in Crenatula, 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. avi- 
cularis, brought from the Antilles by Captain Baudin ; and C. myti- 
loides, which is formed much like a mytilus, and which was found in 
the Red Sea. Ostrea picta, Gmelin, he conceives, may perhaps be a 
variety of this last shell. 
There are very few among the fossil shells of this, or of any other 
country, which, at first sight, are more dissimilar from any of the recent 
shells, than the fossil represented Plate XY. 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 acquainted. The only information which any author yielded 
me respecting 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. 4^7, Fig. 34, h. 
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 analogous to which had been 
till now discovered. 
