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A Sunopsis of the Family of Naiades of North America, with Notes, and a Table 
of some of the genera and sub-ginera of the Family, according to their geogra-, 
phical distribution, ard descriptions of genera and sub-genera. 
By T. A. Conran. Db. 
The present attempt to give a synonymy of the North American Natapgs, | 
has originated from the absence of dates and references in Mr. Lea’s memoirs. “* 
To render strict justice to every authoraccording to date of publication, is not ~~‘ 
only the duty of the naturalist, but a necessity of science. The difficulty in 
the attempt is to ascertain with precision the date of publication of each species,« ~ 
and when this cannot otherwise be obtained, perhaps it would be right to refer 
to the date on the title-page of the volume wherein the species may be described. 
Mr. Lea never refers to the date of publication, but says, “* my memoir bears 
date,” &c., which means, the day it was read before a meeting of a Society, 
though not published in some instances until two years afterwards. In adopting 
the names given by Rafinesque, the rule will be observed to quote no species 
without a mark of doubt, which is not clearly borne out by the description, 
assisted by reference to Rafinesque’s shells marked by his own hand, and now 
placed in the noble collection of Charles A. Poulson, Esq. 
It is true Rafinesque’s descriptions are brief and many of them obscure, and 
his figures rude. Others again are better characterized than some of Lamarck’s. 
Mr. Lea complains that Say has not left him one species in his very short and 
incomplete «Synonymy of Western Unios;”? but on the other hand, Mr. Lea 
credits Rafinesque with only two species of the sixty or seventy he has named 
and described. ; 
Every man must work according to his means and his abilities. Rafinesque, 
in his day, was destitute of the advantages many naturalists now enjoy, and 
could not publish expensive plates ; and, unfortunately, he had the examples of 
Linné and Lamarck for short and indefinite descriptions. If Rafinesque’s 
names should be rejected, there seems no reason why Lamarck’s should not 
share the same fate. 
Of late years, Comparative Anatomy has shown that genera can readily be 
founded on differences in organisation of the animal inhabitants of shells vary- 
ing little in external character, whilst among the Natapgs there are divisions so 
well marked by the external character as well as the hinge, that generic differ- 
ences can be safely predicted to exist among the animals which inhabit them. 
These various genera are moreover not indiscriminately placed in every quarter 
of the globe, but some are peculiar to one country and some to another, as Paxy- 
opon and Prisopon to tropical South America; PLEiopon to tropical Africa, &c., 
and yet an author, even in the present day, is content to arrange the Naiades in 
‘a singularly artificial system, embracing one genus and seven subgenera. Mr. 
Gray’s arrangement is far more natural and useful, but he does not subdivide 
to the extent that Mr. Swainson did, who was the first to give a philosophical 
view of the subject, and to have an idea of geographical distribution of genera. 
Mr. Swainson, speaking of the tuberculated Unios of North America, observes, 
«¢ Where we find a character, however trivial it may appear, pervading a whole 
group, we may be perfectly assured that it is a natural character, although it may 
not be the only one.”? And if this is true of the exterior, a similar uniformity of 
| character in the hinge is still more important; and how strongly marked it is 
de: in Paxyopon, Pier1opon and others! 
| It is supposed that this family existed at as early a period as the Carboni- 
ferous, but it is doubtful if the shells usually referred to Unio were members of 
| this group. Certainly none of the existing genera are represented in the bivalves 
of that era, nor is there any even in the Lower Tertiary; but in the Crag or 
Middle Tertiary, the two genera, Unro and Anoponta make their first 
‘ ; 
4 S 
appearance. 
It is worthy of remark that a genus so nearly related to Unio as Triconta, 
abounded in numerous species in the Oolitic and Cretaceous eras, and then 
ceasing to exist during the long Tertiary periods, reappeared in a solitary species 
of the present day. Is not this long interval between the fossil and recent 
‘ed 
