66 Mr. James Cosmo Melvill oh 



specimen. The left valve is almost flattened, with a broad 

 longitudinal depression, inclining posteriorly, almost down 

 the centre of the left valve from the umbo, the right being 

 convex. Posteriorly in both valves, the shell is quadrato- 

 rostrate, anteriorly oblong, the transverse wavy plicae running 

 concentrically shew this species to belong to that section 

 of the genus of which at present there are only, including 

 this new species, four representatives known to me, viz. : 

 T. magnifica (Jonas), T. plicata (Desh.), and T. granulosa 

 (Ad. and Reeve), the former of them being Californian, 

 the latter Eastern species. 



N.B. — The types of all the above mentioned new species 

 have been deposited in the Mus. Brit., South Kensington. 



