270 Scientific J^otices. 



tion of Mr. Guilding's Ancylus, which make it doubtful v/hether 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 ffluviatilis and laaistris 

 e. g.J 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. It agrees 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 Lymncea 

 and Aplexa this does not exist; though in Planorhis fcorneus,) 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 

 branchise, capable of separating air from water, the animal clearly does 

 not belong to the family Lymnceadce, 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 Lymncea,J I should (with all due 

 deference and respect to his accuracy) be tempted to conceive it possible, 

 that, in so small a subject, and under peculiar circumstances of hght, 

 he may have been deceived, and have taken for a plume of branchiae 

 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" mustof course mean the pulmonary cavity. Besides, 

 I would observe that in Ancylus fiuviatilis, the orifice of the matrix is 



* I had an opportunity of ascertaining beyond all doubt that the animal is 

 hermaphrodite, in September, 1829, at Chedder in Somersetshire. Mr. Lowe 

 has also had the same jood fortune in Madeira. 



