)rous Structure. 455 



occupied as it has been during that period in drawing and en- 

 graving English botany, c\c. in my way to Cambridge 1 stopped 

 long enough at Royston to run up to a chalk-pit, where I picked 

 up a small specimen of this shell, but altogether the most perfect 

 one I have ever met with, with respect to the information which 

 may be obtained from it. A year or two since, the penetrating 

 Miss Benett, of Norton-House, Wilts, collected in abundance 

 some shells very much resembling a sort of muscle, which she sent 

 me, and of which the better specimens were returned after 1 had 

 made such observations as I desired. On returning them, I 

 observed to her, that the hinge might bo discovered if some of 

 the chalk were carefully removed, and I find the hint was taken. 

 At the same time, upon a careful examination and comparison of 

 my own Royston specimen with a few parts of hinges which I 

 had collected together, and which were generally considered as 

 belonging to this shell, I was enabled to determine with accuracy 

 the proper character and situation of the hinge ; from which it 

 became quite easy to see that the difficulty of ascertaining its 

 genus was owing principally to our ignorance of those important 

 points. I now beg leave to lay before this Society the result of 

 my inquiries, and of the comparison of numerous specimens 

 varying in size, shape and locality. 



Genus. INOCERAMUS* 

 Definition of the Genus. An irregular gibbous beaked 

 bivalve shell, of a fibrous structure. Hinge forming a long 

 furrow, transverse to the beak, lateral, linear, divided by 

 numerous sulci across it. Cartilage partly external, partly 

 internal. No visible muscular impression. 



This genus will be found sufficiently distinct from Tenia and 



* Ab 's fibra et xegct[io$ testa. 



3n2 Crenalula 



