1853.] 243 



A Synopsis of the Faintly of Naiades of North Americay with Notes, and a Table 

 of some of the genera and sub-gniera of the Family, according to their geogra- 

 phical distribution, and descriptions of ganera and sicb-genera. 



By T. a. Conrad. 



The present attempt to give a synonymy of the North American Naiades, 

 has originated from the absence of datt^s and references in Mr. Lea's menfioirs. 

 To reader 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 maybe 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 

 Linne 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 Nafades 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- 

 ODON and Prisodon to tropical South America ; Pleiodon 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, althoujjh 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 

 in Paxyodon, Pleiodon 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 Uxio 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, U:<io and Anodonta make their first 

 appearance. 



It is worthy of remark that a genus so nearly related to Unio as Trigonia, 

 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 



