270 Scientific Notices. 
tion of Mr. Guilding’s Ancylus, which make it doubtful whether his shells 
really belong to that family. In the description of the animal he writes 
« Animal unisexuale? Penis? exsertus ad radices tentaculi sinistri. 
“ Branchiarum ramus parvulus prope anum et foramen laterale.’”’ In all 
which points it differs from that of the Ancylus (fluviatilis and lacustris 
e.g.) The species which I have had the best opportunity of examining is 
the first of these.* The animal is hermaphrodite. It has a retractile (not 
exserted) penis, at the base of the left tentaculum. The pulmonary 
cavity, like that of Physa, is on the left side, with a valvular margin, 
in one corner of which is situated the rectum: between this and the foot 
is the orifice of the matrix: the animal breathes air, and is able to swim 
by means of its broad foot. Itagrees with Physa more particularly in 
being a sinistrorsal shell; in the pulmonary cavity being on the left side, 
as also the penis, orifice of matrix, and anus; and in having an auricle or 
pouch at the under side of the base of the tentacula, whereas in Lymnea 
and Aplera this does not exist; though in Planorbis (corneus,) which 
again is a sinistrorsal shell, the auricle is strongly marked. 
Now if what is figured at Tab. Supp. 26. fig 5. b. be really pectinated 
branchie, capable of separating air from water, the animal clearly does 
not belong to the family Lymneade@, which consists of animals coming 
to the surface to breathe air. Indeed, were it not that Mr. Guilding’s 
Ancylus has an exserted penis (if I rightly understand him to mean one 
which is not retractile, as for instance in Lymnea, ) I should (withall due 
deference and respect to his accuracy) be tempted to conceive it possible, 
that, in so small a subject, and under peculiar circumstances of light, 
he may have been deceived, and have taken for a plume of branchie 
the matrix distended with eggs. Fig 5. a. has quite this appearance : and 
in fact Mr. Guilding’s own description favors this view; for his expression 
is “Branchiarum ramus parvulus prope anum et foramen laterale.”’ For 
as he does not seem to have observed the orifice of the matrix, the 
‘¢ foramen laterale’’ must of course mean the pulmonary cavity. Besides, 
I would observe that in Ancylus fluviatilis, the orifice of the matrix is 
* Ibad an opportunity of ascertaining beyond all doubt that the animal is 
hermaphrodite, in September, 1829, at Chedder in Somersetshire. Mr, Lowe 
has also had thesame good fortune in Madeira, 
