136 THE NAUTILUS. 
ists, however, more attention has been given in this direction, and 
while perhaps some have gone to the other extreme and have 
accorded too great importance to the hinge characters, there can be 
no doubt, but that a careful and conservative study of our Amer- 
ican species in this regard would be in many cases a valuable assist- 
ance to the determination of the relations and specific validity of 
many of the at present poorly defined and ill-understood forms. 
In examining some specimens of the common Spherium striatinum 
Lam. recently, I was struck in several instances with the occurrence 
of an abnormal arrangement of the hinge teeth, and was thereby 
iuduced to go further and ascertain if possible to what extent such 
_ irregularities were present. 
My observations thus far have been confined to two species, 
Spherium striatinum Lam., and S. simile Say. Of the former 
species one hundred specimens from twenty-four localities, were 
chosen at haphazard, the number from each locality varying from 
one to eleven. Of these, all the specimens from sixteen local- 
ities, forty-six in number, were normal. Of the remaining fifty-four 
specimens from eight localities, ten were abnormal. In only one 
instance, did more than a single abnormal individual occur in any 
one locality, and in that, three out of nine specimens were abnormal 
and all in the same particular. 
Of Spherium simile Say, sixty-four specimens from nineteen 
localities were examined, the number from each locality varying 
from one to six. Of these, ten individuals out of thirty from eight 
different localities were abnormal. While in those from eleven 
localities, represented by thirty-four specimens, no variation occurred 
In both species the number of abnormal specimens seems surprisingly 
large, amounting to ten per cent in S. striatinum and to nearly 
sixteen per cent in S. simile. In no case was any attempt made to 
pick out unusual specimens and, indeed, no external variation in ap- 
pearance was noticed as being coincident with the abnormal arrange- 
ment of the hinge. 
The normal arrangement of the hinge-teeth of a Sphzerium is as 
follows : 
Right valve Cardinal 1 Ant. laterals 2 Post. laterals 2. 
Left valve Cardinals 2. Ant. lateral 1 Post. lateral 1. 
The variations noticed consisted in the reversing of the position of 
one or more pairs of these teeth. 
