470 Jdfr. G. B. Sower by's Remarks 



valve patelliform, with four internal muscular impressions ; 

 lower valve adhering, nearly flat, with four corresponding 

 muscular impressions, two near the centre, approximating 

 and nearly united, and two near the posterior margin, distant. 

 No hinge. 



Lamarck does not seem to have been acquainted with the ani- 

 mal inhabitant of this genus ; and indeed our knowledge of it 

 must necessarily remain very limited, until we shall have an op- 

 portunity of examining it immediately upon its being taken from 

 its native deeps. All that can be distinguished in the dried spe- 

 cimen are the four ligaments or muscles which attach the two 

 valves together, and the two fringed arms or tentacula. 



It is obvious that this genus differs very materially from Or- 

 bicula, particularly in the manner in which it is attached ; the 

 whole of the lower valve of Crania being firmly attached and 

 adhering closely to the stone, whereas the Orbicula adheres only 

 by an apparently cartilaginous foot, which passes from within 

 through the elongate aperture near the centre of the lower valve, 

 and spreads over a surface of the stone equal to about one-eighth 

 of the surface of the shell. In the appearance of the dried ani- 

 mal very little difference is observable between the two genera. 



Lamarck gives as the type of the genus Crania, the Anomia 

 craniolaris of Linne, a shell which is certainly very little known 

 in this country. I have however seen specimens of it on a coral 

 from the Mediterranean ; and on some of these, the impressions 

 on the attached valve, on account of their having been some time 

 exposed, as I conceive, and being more liable to decomposition 

 than the other parts of the shell, have been corroded away in 

 part, so as to appear rather hollow. I hope it will not be 

 thought irrelevant if I here attempt the characters of the two 

 species of this genus with which I am at present acquainted. 



l. CRANIA 



