BEAKS OF UNIONID^ I/I 



at least, the young shell differs from the adult in all particu- 

 lars except general form. 



A person familiar with the adult forms of a species, say 

 Anodonta fluviatilis, will, when trying to identify the young, 

 naturally appeal to the umbones for some evidence, perhaps 

 the only evidence, to confirm his opinion that he has 

 referred his young shell to the right species. If, by some 

 means, the undulations of the young shell have been eroded, 

 the matter of identification immediately becomes more diffi- 

 cult, and the result, after one has affixed the name to the 

 shell, is looked upon with more or less doubt. With an 

 adult specimen of a described species, any one having access 

 to the literature of the subject may be reasonably sure of 

 being able to come at a correct identification, but with a 

 young shell, one is apt to read description after description, 

 finding, perhaps, a dozen species whose beaks are described 

 as doubly concentric (such as the shell to be named), or 

 undulated and prominent (agreeing with the shell in hand), 

 but finding none described with sufficient accuracy of detail 

 to enable one to reach an exact determination. The finding 

 of a descripion which appears to fit the case does not 

 always remove the stumbling-block of doubt, for in very 

 few cases can one find accurate figures of the undulations of 

 the young shell. This is due in some measure to the fact 

 that species are often described and figured from imper- 

 fect specimens lacking beak characters, and that figures 

 of better specimens have not been substituted for the origi- 

 nal in later works. 



Dr. Lea, in one of his earliest papers in the Transactions 

 of the American Philosophical Society, mentions the charac- 

 ters of the beaks as being of specific importance, and, in his 

 later writings, he has several times called attention to the 

 importance of these characters. With a view to determin- 

 ing for myself the value of the beaks in making specific 

 discriminations, I have carefully examined the beaks of per- 

 fect or nearly perfect specimens of all the Unionidae inhabit- 

 ing the vicinity of Albany. Descriptions and figures of each 



