BEAKS OF UNIONIDiE INHABITING THE VICINITY 

 OF ALBANY, NEW YORK 



By William B. Marshall, M. S. (Lafayette), Assistant Zoologist, New York State 



Museum 



In many of the older works dealing with the Unionidse 

 the decortication of the beaks* is mentioned as being a 

 character of specific importance. Lamarck describes it as 

 a generic character. Many later authors, in describing these 

 shells, pass over the characters of the beaks with only casual 

 mention, styling them prominent, undulated, doubly concen- 

 tric, etc., without directing particular attention to the points 

 of similarity or difference between the beaks of nearly allied 

 species. In many cases the beaks have not been properly 

 figured. 



The beaks of the various species of Unionidse possess 

 characters which are constant and which, in many cases, are 

 sufficient in themselves to distinguish the species. In very 

 young shells the ornamentation of the surface is fre- 

 quently the only reliable means of specific determination. 

 A few of the species of this family have the beaks perfectly 

 smooth but by far the greater number have the beaks more 

 or less roughened, and these peculiarities of ornamentation 

 are not continued in the later growth of the shell, which 

 may become smooth, as in Anodonta fluviatilis, or may 



* The word beak and its equivalent iimbo are usually used to designate the extreme 

 tip or apex of each valve of bivalve shells. In the case of the Unionidse the mean- 

 ing has broadened to include the undulated area near the hinge-line. In this paper 

 it is the broader meaning which is intended when the words beak and umbo are 

 used. 



For an account of the relation between the umbonal tip or glochidium form and 

 the adult form of Unionidse the reader is referred to page 365 of a recent paper on 

 The Phylogeny of the Pelecypoda, by Robert T. Jackson, Ph. D. (Mem. Bost. Soc. 

 Nat. Hist., Vol. iv, No. viii, July, 1890). 



