A. E. Verrill on the Mollusca of Europe and N. America. 5 
or difference of closely allied forms; and no one can claim to 
be infallible in such matters. Some of the errors to be men- 
tioned do not, however, come under this head; for the species 
united have only remote affinities. Nevertheless the naturalist 
who has collected and carefully studied animals in their native 
haunts, under various circumstances, in many localities, and in 
great numbers, has, other things being equal, a very great ad- 
vantage in these matters ; and therefore I believe that Mr. Jeff- 
reys would in most cases agree with me had he collected and 
studied as many American shells as I have, during the past fif- 
teen years, or if he were as familiar with them as he is with the 
British species. In most of the cases to which I refer, my own 
conclusions are in harmony with those of Dr. Stimpson, who 
devoted so many years to collecting and carefully studying our 
shells, and who is well known, for his accuracy in such matters. 
And it would be strange indeed if all American naturalists as 
well as many eminent foreign ones, have always been making 
such ridiculous blunders in regard to some of our most familiar 
shells as Mr. Jeffreys would have us believe. 
Thus he states (p. 240) that “‘ Gemma gemma” (or Tottenia 
gemma) is the young of Venus mercenaria! But it has long 
been known to European as well as American conchologists 
that the animal of gemma is very different from that of mercena- 
ria, and quite peculiar; that the hinge is constructed on a very 
different type is well known; and Prof G. H. Perkins has 
shown (Proc. Bost. Soc. N. H., 1869, p. 148) that gemma is vivi- 
parous, producing about three dozen young, with well-formed 
shells, at one time. Moreover, the young shells of mercenaria, 
smaller than the adult gemma, are sufficiently abundant on our 
shores, and may be seen in many American collections; they 
are certainly very unlike the gemma in form, sculpture, and 
hinge, as has been well known for more than thirty years. 
Again, he states that Arca transversa is a variety of Arca 
pexata, the former being put down as northern, the latter as 
southern. That these shells are widely different in form and in 
the structure of the hinge is well known; for Dr. J. KE. Gray 
many years ago established a new genus (Argina) for the latter, 
on account of its very peculiar hinge. That the animals are 
also quite different I can assert from personal observation. 
Moreover, the differences in the hinge, epidermis, and form are 
remarkably constant; and, finally, the two species have the 
same geographical range from Cape Cod to South Carolina, and 
are often found together. Both are very common in Long 
Island Sound and New Haven harbor; and I have examined 
hundreds of specimens of both species without finding the 
slightest evidence in favor of Mr. Jeffreys’s views. Indeed, they 
are only distantly related, and evidently belong to distinct gen- 
