136 GASTROCIIiENIDiE. 



sentation appears among onr engravings (pi. ii. fig. 8). It 

 is not, however, to be regarded as common, but few 

 localities yielding it in any abundance ; and tlie frequent 

 accidental destruction of its tender valves, during the pro- 

 cess of disinterring it, renders it of course a less frequent 

 sojourner in the cabinets of the collector. Among other 

 localities we may enumerate, Exmouth (Clark) ; off Wey- 

 mouth, alive (M 'Andrew) ; Guernsey, in thick valves of 

 dead oysters (Hanley) ; South Isles of Arran, off Galway 

 . Bay, and Youghal, County Cork (R. Ball). (W. T. Ann. 

 N. H. vol. xiii. p. 434.) 



It is a common inhabitant of the Lusitanian and Medi- 

 terranean, as well as of a great part of the Celtic regions of 

 the European seas, and occurs fossil in the newer pleistocene 

 beds of Italy. Philippi, however, considers the Mediter- 

 ranean form a distinct si^ecies, and describes it under the 

 name of Poliana.^' It was an inhabitant of the British 

 seas during the epochs of the coralline and red crags, but 

 retired for a time, when glacial conditions prevailed. 



SAXICAVA, Fleuriau de Bellevue. 



Shell oblong or rhomboidal, equivalve, more or less in- 

 equilateral and gaping : beaks prominent : hinge furnished 

 with cardinal teeth in some stages of its growth, never with 

 lateral : ligament external, more or less projecting : muscu- 

 lar impressions strong, distant, connected by a sinuated 

 pallial impression. No enveloping tube. 



Animal oblong or claviform : mantle closed in front, 

 except a very small opening for the passage of a digitiform 

 foot, which is furnished with a byssal groove : siphons 

 united nearly to the extremities : branchial and anal orifices 

 large, margined with a fringe of (simple) cirrhi. 



* Wiegmaiiu's Arcliiv. 1845, \>. 18G. 



