Ss 
SP 
* 
Mr. Barnes on the Genera Unio and Alasmodonta. 197 
gitudinally, in this transversely, in that they are crowded and 
mall: in this they are distant and rather large. The ele- 
vated ridge in that is higher and narrower; in this it is 
broader and more depressed ; in that it continues of nearly 
the same. breadth to the base ; in this it diverges at the base, 
to about four times its breadth at the beaks. The shell 
above described has the appearance of age. The tubercles, 
as well as the beaks are much corroded, and the epidermis 
is cracked and broken in many places 
Remarks on the first section, viz. 
* Cardinal teeth, very thick. 
To this section belong the U. Peruviana, rseaietsss and 
obliqua of M. Lamarck, and the U. Cylindricus? of Mr. 
y- The shells in this section bear in cota respects, 2 
resemblance to each other. They are all thick, and have 
avery strong hinge, with, in most oe deeply sulcated 
cardinal teeth, and a cavity under the beaks, more or less 
angular and compressed, extending Wedlar the cardinal tooth. 
They are nearly all waved, wrinkled, or tuberculated on the 
outside. From the last two characters, however, some 
varieties of the U. Crassus are excepted, which have hitless } 
scribed as different species—and that the foregoing are all 
very distinct from each other, so as to be instantly recogniz- 
y even an inexperienced observer—we shall perhaps be 
justified in discriminating the above, and several others also, 
which belong to the next section. 
(To be continued.) 
