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. wetvacea, Chemnitz. 
M. helvacea, Brit. Moll. i. p. 366, pl. 23, f. 2. 
M. glauca, Anglorum. 
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 im 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, Calyptrea 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. 
CYPRINID A. 
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 Astarie Damnoniensis, yet, in the 
forty years we have dredged those localities, neither a living nor 
