“ 
1887] oe Zoology. 287 
abundant in the peninsula, but usually zof rightly nára in cabi- 
nets. It varies greatly in form from typical duryi, which is four- 
whorled, carinated above to the aperture, and has only a fraction 
over one whorl visible on base, to a flatter, more discoidal form 
glabratus Say. Other specimens have the whorl ascending at 
aperture, and, as Say would put it, “labrum horizontally sub- 
rectilinear.” This form is usually marked “ dentus Say” in col- 
lections, sometimes “ corpulentus Say,” but the solidity, polished 
surface, etc., at once separate duryz in all its varieties from these 
shells and from zrivolvis Say. Somewhat malleated specimens 
are also found, and the uptilting of inner whorls mentioned in 
Wetherby’s description is a not uncommon variation in the typi- 
cal form. This species is ae on one hand to g/abratus Say, 
and in other characters approa 
P. scalaris Jay,—a snail which | is placed in a different genus 
by nearly every author who mentions it. After figuring in Palu- 
dina, in Physa, and in the exotic genus Ameria, it may finall 
be located in the Helisoma" section of Cusco: wtth all the fore- 
going species. Although the resemblance of P. scalaris to the 
young of normal Planorbis is quite marked it is probably not 
in any trye sense a case of persistence o f embryonic characters. 
Its derivation from some such discoidal species as the P. duryi is 
more likely.— Harry A. Pilsbry. 
Is Littorina litorea Introduced or Indigenous ?—In regard 
to the question as to whether Littorina litorea is introduced or in- 
digenous, Dr. Dawson has informed the writer of the article on 
sbly earlier. Dr. Dawson says, Torther, that Z. Ltorea “ is and 
has long been widely distributed in Northumberland Strait and 
its vicinity, and that specimens authenticating this may be found 
ey ~~ collections in the Peter Redpath Museum of McGill Uni- 
rsity.” Dr. Dawson believes, from its wide distribution so far 
naire that “it is a — and probably aboriginal member of. 
the fauna of Acadi 
It is with great diffidence that the writer ventures to disagree 
with so thorough a student of these matters as Dr. Dawson. 
But he is unable to see that anything is proven by this new ad- 
dition to our knowledge of the distribution of the shell, except 
that it Ated ppor our shores earlier a more wey spread than 
di 
al large American species which have thei inner pias of pine sharply 
Ba, ba the la whether the a be rounded or angular in the adult. „All the 
F placed in the typical section of Planorbis in Land and Fresh-Water Shells, 
Il., except Aavanensis and liebmanni, which I have elsewhere shown to belong 
in Segmentina, and Subcrenatus Cpr., belong in the section Helisoma. 
