K) On Trichites, a fossil genus of Bivalve Mollusks. 



guishable; the terminal umbones arc very much curved and 

 turned forwards. The planking beds of the Great Oolite at Min- 

 nhinhamptop Common and freestone of the Inferior Oolite near 

 to the same locality produce it, but it has not been recognized in 

 the upper portion of the Inferior Oolite ; from the intractable 

 character of that rock, however, this circumstance must not be 

 considered as conclusive of its absence. Our examples in point 

 of size convey but a very inadequate notion of the magnitude 

 often attained by the genus; but it would appear that the larger 

 sections belong to the second, or possibly even to a third and 

 more gigantic species. The Pinna Saussurei (Pinnegene of Deluc) 

 is distinct from our Cotteswold shells ; his figures, taken from 

 specimens broken and partly enveloped in the stone, do not con- 

 vey any precise idea of the external form, but the portion which 

 exhibits the character of the surface is altogether different. 



Trichites undatus. 

 (Inferior Oolite.) 



Shell oblong ; umbones . . . . ; ribs obscure, few, concentric, irre- 

 gular and undulated, sometimes obsolete in the larger valve. 

 The smaller valve unknown. 



Length 9 inches, breadth 7\ inches. 



The only well-preserved example in our possession has lost the 

 terminal extremity, but in other respects is nearly perfect ; the 

 hinge-line is more nearly horizontal than in the T. nodosus, and 

 the entire form is less convex ; the other valve, though attached, 

 cannot be cleared from the hard matrix. It occurs abundantly 

 in the upper ragstone of the Inferior Oolite, a rock which usually 

 defies all attempts to separate the shell in a tolerable condition ; in 

 this instance a large portion of the surface fortunately coincided 

 with the natural parting of the bed. 



