MACTRA. 107 



littoral species, while the M. elliptica is never taken, except by 

 the dredge in the coralline zone, six miles from the shore. 



M. HELVACEA, Chemnitz. 



M. helvacea, Brit. Moll. i. p. 366, pi. 23. f. 2. 

 M. glauca, Angloruin. 



This splendid shell is not British. We have the authority 

 of the French oystermen who bring cargoes of oysters into 

 the port of Exmouth, to plant in the parks, on the Exe, at 

 Lympstone, that it does not even inhabit the Guernsey or 

 Jersey grounds, and that it is a French littoral or laminarian 

 species, and only taken on the in-shore oyster-beds. We have 

 often procured it, the Pileopsis hungaricus, Calyptr&a sinensis, 

 and large Guernsey Chitons, by overhauling the cargoes. Dead 

 valves have been taken on our coasts, either cast thereon by 

 storms or from discharged ballast, a fertile source of spurious 

 species. Near thirty years since, Miss Pococke, daughter of 

 Admiral Pococke, the original assigned authority for this 

 species as British) in person, at Bath, presented the author 

 with two pair of the M. helvacea, taken by herself on the 

 extensive sandy districts of Cornwall ; but she by no means 

 guaranteed their being indigena, and with perfect frankness 

 stated every particular of their acquirement, which scarcely 

 admitted a doubt of their being aliens to Britain. 



CYPRINHXE. 



This family consists of four genera, Cyprina, Isocardia, 

 Circe, and Astarte ; the first three have only one species in 

 each, and Astarte six or seven. We have described Cyprina, 

 Isocardia, and Astarte. With respect to Circe, it has not 

 occurred to us alive ; but in the essentials of family configura- 

 tion, of there being no cicatrix in the pallial impression, 

 showing that the tubes or orifices are short or sessile, it 

 agrees with its congeners. It is remarkable that the coasts 

 of Devon give name to the Astarte Damnoniensis, yet, in the 

 forty years we have dredged those localities, neither a living nor 



