52 
THE NAUTILUS. 
reality of the distinction between the mass of southern, and the 
northern specimens of P. appressa. The northern shells described 
by Say have no incised spirals whatever, and the upper lip-tooth is 
frequently developed. The southern specimens (which we have 
called P. appressaperigraptd), have spiral incised lines more or less 
developed, and the upper tooth is wanting in the vast majority of 
cases. When it is present, as in the Cherokee Co., N. C. examples 
mentioned by Mr. Wetherby, I would regard it as an interesting 
case of reversion. 
As to Polygyra tridentatci, Mr. Wetherby has not read my paper 
with sufficient care to see my meaning. He attacks my P. fraudu¬ 
lent, but says in the next sentence that P.fallax is perfectly distinct 
from tridentata. The truth is that Helix fallax of Wetherby and 
other modern authors and collectors is identical with my fraudulenta ! 
The true H. fallax of Say is identical with H. introferens Bland, as 
I have already stated in this journal and elsewhere. So my critic 
discredits and affirms the validity of this form in one article! As 
to P. tridentata edentilahris, Mr. Wetherby has evidently never seen 
it. The var. juxtidens is a well-known form. I believe it to be a 
distinct line of differentiation, well worth attention and recognition 
by name. 
I have not referred in this article to the large class of individual 
variations such as is shown in the banding of many Helices. This 
mode of variation is often repeated, different species having parallel 
modifications. The mutations are frequently not inherited, any of 
the forms giving birth to numerous others, as is the case with the 
band-varieties of Helix nemoralis. This tendency to “ sport ” in all 
directions is a totally different thing from the moulding of an entire 
race explained above ; and its products cannot usefully be given 
varietal names. They are best expressed by formula; devised to 
cover entire classes of such variations. 
TYPES OF ANODONTA DEJECTA REDISCOVERED. 
BY CHAS. T. SIMPSON. 
In making a final arrangement of the general collection of Union- 
idee of the National Museum I found the other day among some 
