96 Quarterly Joitmal of Couchology. 



constitute two distinct genera. As illustrations, he gives Helix 

 obvolida, and some of the Vertigoes, which differ from other mem- 

 bers of the genera in being toothed or notched. Reeve 

 separates them, and says of Azeca " that it is a mollusk of different 

 distribution and habit, and the shell has a totally distinct typical 

 structure." (p. 94.) — On the other hand, Jeffreys makes 2 distinct 

 genera Balia and Clausilia, because the latter has a ckusilium, or 

 twisted internal plate, and has also oblique teeth or folds which 

 contract the aperture of the shell. In Balia, the clausilium is 

 altogether wanting, and the mouth has no teeth or folds, though 

 it is sometimes furnished with a tubercular tooth, formed in the 

 columella or pillar. In the genus Piano? bis, I mention the two 

 species, carinatus and complanatus. This latter shell may be 

 distinguished from the former, as Jeffreys says (p. g2)—" By its 

 narrower and more rounded whorls, as well as by the keel being 

 placed below, instead of in or tOAvards the middle of the periphery. 

 It is usually larger and thicker, and is more generally diffused and 

 plentiful." He also gives a variety o( carinatus viz. disciforinis, 

 which is often found mixed with the \di%\.( carinatus)." (Linn Trans, 

 Vol. xvi., p. 385, by Jeffreys) and of which he says, "The shell is 

 flatter and thinner, of a yellowish colour, having the last whorl 

 larger in proportion to the others, and the keel more prominent 

 and sharp, and placed exactly in the middle." (p. 90.) He alsO; 

 says (p. 92), "That carinatus and complanatus, are connected to-; 

 gether through the P. submajginatus of Cristofori and Jan, alias 

 the P. intermedins of Charpentier." — Mr. Alder, speaking of 

 disciform is and carinatus, says, " I cannot perfectly understand the 

 distinction between them." (Gray, p, 239). ^o\n \i carinatus ?Lr\.^ 

 complanatus are ranked as two species, mainly owing to the differ- 

 ence in the position of the keel, why is not disciforniis in which the 

 position of the keel is as different from either ol these two, as they 

 are from each other — also ranked as a third species ! But it seems 

 to me that as it is not so considered, if we apply Mr. Jeffrey's own 

 test, one of these two must give way as a species, and be considered 

 only as a variety, for these three shells certainly appear to me, by 

 his own language (A), " to be so intimately blended together by 

 the intermediate links as to make the Hue of separation too critical," 

 and therefore the test fails, so that taking P. carinatus as the type, 

 the other two, namely, cofnplatiatus and disciforniis, can only be con- 

 sidered as varieties of it.* 



In the genus Limncea, we meet with some very striking differ- 

 ences in the species, but which, for some cause or other, only 

 entitle the owners to be considered as varieties. Then of Z. peregra 



Note. — In speaking of the Helix ncnioralis and hortensis, Jeffreys considers 

 that the variety hybrida connects the two, and that therefore they are not 

 distinct species ; but here, although P. carinatus and complanatus have an 

 intermediate form in disciforniis, it is in this case not allowed to make anj 

 difference, and the two species referred to remain as distinct. 



