BIVALVIA. 165 
Puowas crispata, Linn. Crag Moll., vol. ui, 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. 
Puonas crtinprica, J. 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 Plolas 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 Piolades 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 Pio/as returns upwards to the water by the pressure of 
the foot, as the So/en 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. 
