NEWTON: MOLLUSCA.N REMAINS IN BRITISH KEUPER. 4II 



The specimen figured is in the collection of the Rev. P. B. 

 Brodie, of Rowington, Warwickshire. 



Pholadomya (?) Richards! sp, nov. 



The specimen represented by fig. 2 (drawn twice natural 

 size), exhibits an impression of a left valve of a transversely 

 elongate and oval-shaped shell ; it is, besides insequilateral in 

 contour, having the umbo placed anteriorly. The cardinal 

 margin slopes gradually down each side, whilst the ventral line 

 is much curved. The surface ornament consists of a series of 

 cost^ or ribs radiating from the umbo and extending without 

 interruption over the entire valve including the anterior and 

 posterior areas. These ribs are coarser and straighter in the 

 centre, but become slightly concave in their descent, closer and 

 somewhat finer over the terminal portions of the shell. There 

 are no indications of lines of growth crossing the costae. 



Dimensions. — 23 mm. in length by 11 mm. in height. 



Observations. — This specimen bears a general resemb- 

 lance to an Aira or a Cardvan, but in both these genera the 

 tests are usually too thick for their external sculpture to be 

 observed within the valve ; and in their casts only muscle 

 marks and pallial impressions would mostly be seen. We must 

 therefore regard our shell as having possessed an extremely 

 thin-tested structure such as exists in Pholadomya. Although 

 it is rather rare for Pholadomya to exhibit radiating ribs over 

 the whole posterior area, we can cite a precedent in Agassiz's 

 species P. midticostata'^ from the Portlandian rocks of Switzer- 

 land, where the entire valve is ornamented in this manner. As 

 a provisional arrangement, I shall, therefore, refer the Keuper 

 shell to this genus, and name it Pholadomya (?) Richardsi. 



This specimen (fig. 2) was obtained by Mr. E. P. Richards, 

 and is now in the Geological Museum at Jermyn Street (No. 



' E'tudes Critiques Mollusques Fossiles (Myes), 1842, pi. 2 m, fig. 8, p. 52. 



