14 ROCHESTER ACADEMY OF SCIENCE. [Oct. 26, 



Class PELECYPODA. 



The L'nionidcX form a large and distinct group in this class of 

 Mollusca and are generally known under the common names of 

 "river clam," or "river mussel." 



Dr. Lea, the great authority on this interesting family, enumer- 

 ates over eleven thousand recent species and divides them into nine 

 subgenera ; three of which, Unio^ Margaritana and Anodonta are rep- 

 resented in the United States by about seven hundred and thirty 

 species ; a little over one half of the whole number. 



There is scarcely a lake, river or creek in this broad country but 

 can furnish some specimens of this bivalve, and often a mere stream- 

 let that one may step over has become the habitat of one or more 

 species. Monroe County having a lake frontage bounding it on the 

 north, with several bays, inlets and creeks ; the Genesee river flowing 

 from the southward ; and the Erie canal winding through from west 

 to east with its own special fauna, furnishes at least thirty species of 

 this family. 



The shells of these molluscs, like bivalves generally, are dis- 

 tinguished by the presence, number and character of certain processes 

 called teeth, which interlock each other under the apex and dorsal 

 margin. In the Unio there are 1.2 or 2.2 central, and 1.2 lateral 

 teeth ; in Margaritana 1.2 central and no laterals; and in Anodonta 

 the teeth are absent or almost obsolete. By these features we may 

 determine the genus of a so-called river mussel. (See plate 8, figs, i, 

 2, 3.) 



River and lake fishing for these molluscs is best accomplished 

 with a row boat and hand net in the fall of the year, when the water 

 is low and the shells have attained the season's growth. The most 

 favorable time for canal work is in the spring as soon as weather will 

 permit, it being customary every year about the month of March to 

 run off the water in order to make any necessary repairs, leaving only 

 a foot or so of mud and water at the bottom. At such times whatever 

 the canal contains can be easily seen and secured. It is a delightful 

 pastime in the sunny days of early spring to traverse the canal and 

 follow in the wake of the musk rat, and if possible forestall him in 

 the appropriation of some choice living specimen ; for a shell to be 

 perfect should be taken alive, before the rat has made his dinner of 

 it or the sun has bleached the empty shell. 



