﻿BIVALVIA. 



165 



Pholas crispata. Linn. Crag Moll, vol. ii, p. 296, Tab. XXX, fig. 9. 



Localities. Red Crag, Walton, and Sutton. Lower Glacial, Belaugh. Middle 

 Glacial, Hopton. Upper Glacial, Bridlington. Post-glacial, Kelsea Hill and March. 



As just explained, the reference by me of this shell to the Cor. Crag was a mistake for 

 the above Ph. brevis. Fragments of a large Pholas are common in the Middle Glacial 

 sand of Hopton, and, I think that there is little doubt of their belonging to this species ; 

 but it cannot be so affirmed with certainty. Mr. Jeffreys gives it (in fragments) from 

 Kelsea Hill, and a fragment probably of this species has occurred at March. None of 

 the specimens that I have seen indicate a magnitude of more than three inches. 



Pholas dactylus is mentioned by Mr. Alfred Bell in ' Ann. and Mag. Nat. Hist.,' 

 Sept., 1870, as from the Red Crag of Walton Naze, and Mr. Jeffreys has, on that 

 authority I think, inserted it in his list to Mr. Prestwich's paper. Mr. Bell has not 

 been able to find the specimen. 



Pholas cylindrica, /. Sow. Crag Moll., vol. ii, p. 295, Tab. XXX, fig. 8. 

 Localities. Red Crag, Sutton and Walton Naze. 



I stated in the ' Crag Moll.' that fragments of this shell occurred in the Coralline as 

 well as in the Red Crag ; but it now appears to me that these fragments belong to 

 Ph. brevis and not to cylindrica. 



Pholades are spoken of by Sir Charles Lyell in the ' Lond. and Phil. Mag.,' August, 

 1835, p. 82, as having been found at the depth of six or eight feet below the surface of 

 the Cor. Crag at Sutton where not covered by Red Crag. Mr. Charlesworth, also, speaks 

 of specimens of Pholas crispata occurring in the sand of the Cor. Crag at the depth of 

 three feet from the surface ; and I have obtained a specimen of the same species from the 

 same locality at nearly four feet from the surface. In the interior of these specimens 

 there was no Coralline Crag, but instead of it fragments of what appear to be Red Crag 

 shells. 



If these specimens found buried in the material of the Coralline Crag belong, as I 

 presume they do, to the age of the Red Crag, it is evident that Pholades excavate to a 

 depth beyond what they have hitherto been supposed to do, and that either these 

 tubular excavations are by some means kept open to the surface so as to allow of the 

 access of water, or else that the Pholas returns upwards to the water by the pressure of 

 the foot, as the Solen does. The foot, however, in Pholas does not much resemble the 

 same powerful organ in Solen, by which that genus is enabled to rise through the sand 

 to the water. 



