122 THE CHICAGO ACADEMY OF SCIENCES. 
deferens in a depression on the side of the large sac below (which is 
believed to be the penis) would seem to indicate that it could not be 
co regarded. The vas deferens forms a loop exterior to the male or- 
gan, one end entering the penis in a depression on the side, the other 
end entering at the junction of the penis and the appendage, reap- 
pearing at the apex of the latter, whence its course is the same as in 
Lymnea, directly to the penial opening. There is no division of 
muscles retracting the male organ in Planorbis as in Lymnea, the 
penis in Planorbis being retracted by a wide, thin band of muscular 
tissue which is inserted in the columella muscle near the left buccal 
retractor, the characteristic penis retractor of Lymnea (pl. X, A, RM) 
being absent. It would be of great interest and value to know pre- 
cisely the office of this peculiar appendage, but whether it prove to be 
the true penis (and the organ below the penis sac) or an appendage of 
the penis, does not alter the fact that its position on the penis and 
the peculiar insertions of the vas deferens provide a characteristic 
difference from Lymne@a which is of family value. The principal 
characters which differentiate Planorbide from Lymneide are the 
peculiarities of the male organs, the bicuspid central tooth (plate XIII, 
B) the planorboid, discordal shell and the filiform tentacies. 
The taxonomic value of the groups Camptocerinze and Pomphola- 
gine of Dall, cannot be predicated at the present time, fresh material 
not being available. Dall’s figure of the genitalia of Pompholyx* 
is not in sufficient detail to allow of an opinion. The central tooth is 
bicuspid, which indicates relationship with Planorbis. 
As thus restricted, the Lymnzide present a homogeneous group 
of snails which may be divided into several genera and subgenera. 
Before entering upon a discussion of the data upon which these groups 
are based it may be of interest to review briefly some of the previous 
classifications of the Lymnezids which bear directly upon the Ameri- 
can fauna. All of these have been based on shell characters. 
In 1840, S. S. Haldeman monographed the genus Lymnea, includ- 
ing as subgenera Limnea, Radix, Leptolimnea, Bulimnea and Acella, 
the last two being described as new. 
In 1865 W. G. Binney monographed the genus, recognizing the 
following groups as subgenera: 
Limnea Lam., Radix Montf., Bulimnea Hald., Limnophysa Fitz., Leptolim- 
nea Swains., Acella Hald. 
1Ann. Lyc. Nat. Hist., IX, pl. 2. 
