ANCYLUS. 123 



species of Conferva, in the Baltic Sea. According to 

 Mr. WhiteaveSj it hibernates between the sheathing 

 leaves of Sparganium ramosum. 



This species is easily recognizable from A. fluviatilu- 

 by its different habitat and the oblong shape of its shell, 

 as well as by the form of the beak, which is twisted 

 decidedly to the left, instead of being (as in the other 

 species) nearly central or inclined to the right. 



It has been called by some authors A. oblongus, being 

 the specific name given to it by Lightfoot under the im- 

 pression that this was not the Patella lacustris of Linne. 

 There can, however, be scarcely any doubt that Linne 

 meant this species, and not A. fluviatilis, because in his 

 ^ Fauna Suecica ' he mentions its being rather common 

 in lakes and attached to the submerged leaves of aquatic 

 plants, especially of Stratiotes. His description of the 

 shell is applicable to either species. 



Nearly half a century ago, a curious instance of false 

 analogy occurred with respect to an organism which 

 Draparnaud described and figured (in his admirable 

 History of the Land and Freshwater MoUusca of France) 

 as " Ancylus spina-rosce'^ from specimens sent him by 

 Ferussac. These specimens were afterwards discovered 

 not to be testaceous; and many conjectures were from 

 time to time made as to their nature. It was supposed 

 by some that they were parts of a small pod or capsule, 

 by others that they were the bracts of a flower-stalk, and 

 by not a few naturalists that they were scales of a fish. 

 The puzzle, however, was at last solved by the discovery 

 that these nondescripts were the valves of a Cyjjris, and 

 therefore belonged to the Crustacea. 





