172 BULLETIN OF THE NEW YORK STATE MUSEUM 



will be found in this paper. A study of the shells of such a 

 limited area cannot lead to any broad conclusions and such 

 conclusions as are drawn must necessarily be of local appli- 

 cation. The following statement may be made as being 

 applicable to all the species found in this vicinity : — They 

 have the beaks ornamented with undulations of the surface, 

 and these undulations are constant in each species, and are 

 sufficient in themselves to distinguish each from every other 

 species inhabiting this neighborhood. 



For practical purposes of identifying adult specimens the 

 beaks are of little value in some species as they are usually 

 eroded to such an extent as to have lost all trace of their 

 original appearance, and, in most cases, the adult characters 

 are sufficiently distinct to determine the species. With 

 young shells the case is different. The undulations are rarely 

 eroded to such an extent as to have lost their distinctive 

 characteristics, and, as has been said, the undulations are in 

 some cases the only sure means of identification. 



Among the characters which are common to the beaks of 

 most species should be mentioned here the fine concentric 

 striae which crowd the surface of the young. In the follow- 

 ing descriptions no notice of this character will be taken 

 unless some variation worthy of particular mention be ob- 

 served. It may be remarked that these striae are merely 

 upon the epidermis while the undulations are in the cal- 

 careous matter of the shell. The striae do not run parallel 

 with the undulations but parallel with the nearest growth 

 lines of the shell and necessarily they cross the undulations. 

 In a less marked degree the striae may be seen throughout 

 the growth of the shell to the adult state. 



Another feature which may be said to be common to all 

 the species is the location of the highest and broadest por- 

 tion of each undulation. It is on the ridge running from the 

 beak to the posterior ventral angle of the shell. This ridge 

 represents the line of maximum growth of the shell so that 

 the undulations of the beaks in their line of maximum growth 

 coincide with the line of maximum growth of the shell. 



