Mr. Barnes on the Genera Unio and Alasmodonia. 109' 



making these varieties, different species? We have examin- 

 ed shells from the localities mentioned by M. Lamarck, and 

 compared them with his descriptions, and, if we do not mis- 

 take, he has fallen into the error of making distinctions with- 

 out a specific difference. But, even if this is admitted, we 

 sha'l not be disposed very severely to censure, so long as 

 anatomical dissections have not been, and in many cases 

 cannot be called in to decide the question ; for it is, after 

 all, upon the knife that we must depend for perfect accura- 

 cy in this and similar cases. In the mean time, it has 

 been agreed upon by naturalists, to arrange these ani- 

 mals by their shells; presuming always that a different 

 form and fig'ire of covering belonged to an animal of 

 a different organization. It is impossible to decide wheth- 

 er they are "the common children of common parents," or 

 otherwise. This is a case precisely similar to that which 

 occurred between Linnaeus and Lamarck concerning the 

 Olives. "The former expressed a doubt whether there is 

 niore than one species of the Olive, and the latter has des- 

 cribed ffty-nine."* 



In most cases wherever M. Lamarck can find a differ- 

 ence, though by his own account, '^nothing remarkable,^' f 

 he makes a different species. Too many as well as too few 

 distinctions undoubtedly defeat the object of the Naturalist, 

 which is to make his readers acquainted with the produc- 

 tions he describes. In the present state of our knowledge 

 we cannot perhaps do better than to take a mean course, 

 and where the discriminations are sufficiently obvious, in 

 important parts and essential particulars, to apply a different 

 specific designation. This course has been attempted in the 

 following notice of undescribed species. We have had the 

 opportunity of examining and comparing a great number of 

 specimens, and very rarely have we given a new specific 

 name to a solitary individual. In cases where the contrary 

 has, from necessity, been done, the specimens were by no 

 means of a dubious character; but healthy, well-grown and 

 perfect individuals, so strongly marked and distinctly char- 

 acterized, as to leave no doubt. 



* Dillwyn, page 314. 

 t See TT. Gaor'rina and Glabrata of Lnmarck 



