THE NAUTILUS. 115 



less. But it must be stated that, in the first place, two or 

 several manifestly distinct species may show the same essen- 

 tial hinge characters, as e. g. P. compressum, supinum, 3 frau- 

 dulentum, forms of variabile, aquilaterale, and one or two 

 others, so that they could not be recognized with certainty 

 by the hinges alone; in amnicum and dubium the hinges are 

 practically alike ; and the same must be said of species of 

 some other groups. Consequently it is necessary to consider 

 other features also, and upon careful and judicious examina- 

 tion it will be found that they are not worthless. 



In some species the hinges are quite peculiar, with features 

 seen in no others, just as there are some characteristic and 

 recognizable irrespective of their hinges. 



On the other hand, in examining numerous specimens it 

 will be found that the hinge also shows more or less of varia- 

 tion in most of the species. A description carried to minute 

 details, as thus postulated, is liable to disrupt an actual 

 species the hinge of which is variable. And to state again: 

 if the hinge alone is considered in establishing and recogniz- 

 ing species, regardless of other features, manifestly distinct 

 species will be "lumped" into one. 



Even Baudon, '57, p. 17, came to the conclusion that dif- 

 ferences of the hinge and its teeth are applicable for the dis- 

 tinction of groups, but not of species and varieties. "It is 

 consequently necessary to rely on other features also in order 

 to separate each type. ' ' 



Literature Cited. 



BAUDON, AUGUSTE, Essai Monographique sur les Pisidies 



Franqaises. Paris, 1857. 

 BERNARD, FELIX, Premiere (to Quatrieme) Note sur le de- 



veloppement et la morphologic de la coquille chez les 



Lamellibranches. Bull. Soc. Geol. France, ser. Ill, tome 



XXIII & seqq., 1895-1897. 

 CALL, E. E., A Descriptive Illustrated Catalogue of the Mol- 



s supinum comes very close to compressum. 



