Mr. Barnes on the Genera Unio and Alasmodonta. 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 
shall 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 
all, upon the knife that we must depend for perfect accura= 
ey 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 figure of covering belonged to an animal of 
a different organization. It is impossible to decide or 
er they are “the common children of common parents,” 
otherwise. This is a case precisely similar to that liek 
Lama 
occurred robink Linnaeus and rck concerning the 
Olives. rmer expressed a doubt whether there is 
more than eae species of the Olive, and the latter has des- 
cribed fifty-nine.”* 
n most cases wherever M. Lamarck can find a differ- 
ence, though by his own account, ‘nothing remarkable,’’+ 
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 deseribes. 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 — ars, to apply a different 
. Specific designation. This course has been attempted in the 
following notice of edie a 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 rit marked and distinetly char- 
acterized, as to leave no dou 
* Dillwyn, page 514. 
+See U, Georgina and Glabrata of Lamarck. 
