XXV111 synopsis or 



In regarding these outlines, the shell is supposed to he lying on its side with the 

 ligament furthest removed from the observer, and the beak to the right of it. The 

 base will, of course, be nearest to him, and the anterior margin will be to his right, 

 while the posterior margin will be to his left. This is my mode of arranging my 

 whole cabinet, which contains over 9500 specimens of this family, each differing in 

 sex, age, some characteristic, or in geographical distribution. 



In attempting to make a complete synopsis of the Uniomdce, much labor has 

 necessarily been expended. I do not present this as a perfect work, but it has been 

 made as nearly so as the opportunities in my possession permitted. Errors may have 

 arisen from two sources: first, default of judgment; second, from accident, owing to 

 the mass of research necessary to accomplish the object, considering the crude state 

 the subject has been in. I shall be most agreeably disappointed if there be not parts 

 pointed out as erroneous which are substantially correct. It will be observed that 

 the works of M. Rafinesque are but little quoted. This has arisen from the utter 

 impossibility of satisfying myself as to his species, causing me at an early period to 

 abandon the task of making out his very imperfect descriptions. His own discrep- 

 ancy in the names sent to Ferussac, 1 and those which are attached to specimens here, 

 together with the want of accordance in the tables made out by his friends, have 

 induced me to regard his claims as being too slender to rely upon the decisions, so 

 contradictory, of the several parties, in the absence of the individual specimens noted. 

 In the absence of these specimens, which no naturalist has, I believe, ever seen but 

 the Professor, I feel myself compelled to prefer other authorities, which are now 

 almost universally received by our malacologists. I am the more fortified in this 

 conclusion, when I see that Mr. Conrad, his most ardent advocate, acknowledges that 

 he (Rafinesque) has made six species from a single one; 2 and the absurdity is still 

 stronger when we turn to M. Rafinesque's monograph, and find that this single species 

 has furnished several genera, and is placed, in fact, in two different sub-families 1 1 1 



How far M. Rafinesque ought to be considered worthy of authority at home and 

 abroad may be understood by the opinions of the following distinguished writers. 



The late Dr. Binney, in his admirable work on "Terrestrial Mollusques of the 

 United States," says the papers of Rafinesque " are not deemed worthy of any con- 



1 " Les erreurs involontaires qui e'ehappent a M. Rafinesque dans ses envois augmentent aussi la 

 difficulte - de reconnaitre ses espeees. Nous avons re§u de lui les meraes coquilles sous diffe'rents noms, et 

 d'autres avec des noms evidemment autres que ceux qu'elles portent dans sa Monographie. II en est 

 result^ une difficulte inextricable pour la determination de ses especes, et pour pouvoir etablir une syno- 

 nymie exacte entre lui et les autres qui, depuis, se sont occupes des Mulettes." — Magasin de Zoologie, 

 1835, Class v., Nos. 59 et 60, p. 13. 



2 U. triangularis. Conrad's Synoptical Table of New Fresh Water Shells of the United Slates, p. 72. 



