LIMNJEUS. 207 



tudinally, and generally crossed by raised transverse 

 lines, giving it an angular appearance like cut glass ; 

 pillar with the fold very strong, forming a slight um- 

 bilicus, the lip white and spread. 



These shells vary greatly in thickness, according 

 to the nature of the water they inhabit. The outer 

 whorl of the adult shell is often very gibbous. These 

 variations have caused the animal, when found in 

 clear quiet water, to be considered as a separate 

 species. 



Dr. Turton's figure (Marc. ed. 1. f. 102.) of Physa 

 scaturiginum has been suspected to represent a young 

 individual of this species. It is a copy of Drapar- 

 naud's, which is a very doubtful species ; and thought 

 to be the young of some land shell. A reversed dis- 

 tortion is sometimes found. (Hanow Seltenheiten, ii. 

 t. 1. f. 5.) 



Montagu erroneously thought that these animals 

 were unisexual ; for he observes, the sexes, too, are 

 distinct, as is usual in aquatic Limaces. 



The eggs are ovate, with a yellow spot ; they are 

 united together into elongated subcylindrical or 

 oblong masses, attached to water-plants, &c. (See 

 Pfeiffer, f. 13, 14, 15.) 



Rossmasler has described a North American 

 species, like the first variety, under the name of L. 

 speciosus. (t. 2. f. 50.) 



M. Prevost has remarked that the impregnation 

 of these animals is only accomplished by the par- 

 ticipation of three individuals ; the middle one 

 using the functions of both sexes, the two others 

 that of the male and the female only. Sometimes the 



