SPH^NIA. 193 



Individuals exceeding a quarter of an inch in breadth, 

 and four-ninths of an inch in length, must be regarded as 

 fine and uncommon examples. But the relative proportions 

 of length and breadth vary considerably in different speci- 

 mens ; occasionally, the former is greatly increased by the 

 under side being so produced (in which case the posterior 

 termination is much attenuated) as to resemble a dwarf 

 Mya truncata with its tube attached. Indeed, it has been 

 supposed that the present shell is only the fry of the above- 

 mentioned bivalve ; but, having examined the several 

 stages of Mya truncata, we positively state the contrary, 

 the likeness being confined to the truncated outline of the 

 adult : neither is there any possibility of confounding it 

 with the young of M. arenaria. 



Very solid and aged single valves of the common oyster 

 seem its favourite burrowing place, from which habitat 

 it has been taken in comparative abundance (for so rare 

 a species) near St. Peter's Port, Guernsey (S. H.); at 

 Torquay it is occasionally found in limestone, dredged 

 in company with Gastroch(En(e. from about ten fathoms 

 depth (S. H.); it is obtained likewise at Scarborough 

 (Bean); Isle of Man, on both north and east coasts, in 

 from twelve to twenty fathoms (E. F.); in twenty-five 

 fathoms, eight miles from the north coast of Anglesey 

 (M' Andrew and E. F.) ; at Tenby, and in the vicinity 

 of Swansea (Jeffreys). 



" Two valves were found at Bray by Mr. W. H. Har- 

 vey" (Thompson); Frith of Forth (E. F.). 



Mr. M'Andrew (who has taken it likewise in Spain) 

 procured it also from the Frith of Clyde. 



VOL. I. c c 



