PLANORBIS. 491 



bases of the tentacula ; edges of mouth honey-yellow ; motions 

 sluffo'ish. 



Found abundantly in all our ponds, small brooks, and stagnant 

 pools. 



This is a somewhat darker shell than P. trivolvis, and is distin- 

 guished from it by its left side and its aperture. The cup of the 

 left side is less smooth and regular, and is not bounded by the sharp, 

 elevated line ; when this shell is laid upon its right or upper side, 

 the lip of that side will scarcely touch the plane on which it lies, 

 while, in P. trivo/vis, tlie shell would be lifted by the lip ; the aper- 

 ture has not the sharp angle of the left side, produced by the termi- 

 nation of the carina, but in the young stages it is difficult to distin- 

 guish the two. It is very closely allied to P. corneus of Europe ; 

 but in that shell the left side is scarcely concave, and the suture is 

 deep ; the aperture is nearly orbicular, being almost equally rounded 

 on both sides. 



This shell has hitherto generally borne the name of P. trivolvis 

 in New England ; but it is not the trivolvis of Say, and is either his 

 P. lentus or a new species. 



[Professor Haldeman refers it to P. trivolvis^ var. fallax. In the 

 "Land and Fresh- Water Shells," Part 1., I refer it to P. trivolvis. 

 It is not the lentus of Say. 



Planorbis bicarinatus. 



Fig. 134. 



Shell deeply concave on both sides ; whorls three, strongly carinated on both 

 sides ; aperture abruptly arched at the carina of the left side, its lip extending far 

 beyond the plane of the pi-eceding whorl. 



Planorbis bicarinatus, Say, Nich. Encyc. pi. 1, fig. 4 (1817, 1818, 1819) ; Am. Conch. 6, 

 pi. 54, fig. 3 (1834) ; Bixxet's ed. 44, pi. 54, fig. 3, pi. 69, fig. 4. — Mrs. Gray, Fig. 

 Moll. An. pi. 310, fig. 1. — Haldemax. Mon. vii. 6, pi. 1, figs. 1 -6 (1844). — Ad- 

 ams, Shells of Vt. 155 (1842). —I)e Kay, N. Y. :\Io11. 60, pi. 4, fig. 63 (1843).— 

 GocLD, Inv. of Mass. 203, fig. 134 (1841 ). — Ciiemn. 2d. ed. 56, pi. 60, fiijs. 11 - 13. 

 — PoTiEzetMiCHAUD, Gal. des Moll. i. 207, pi. 21,fiirs. 1 -3. — Anon. Can. Nat. ii. 

 204, fig. (1857). — W. G. BiNNEY, Smith. Inst. L. and Fr. W. Shells, ii. 123, figs. 

 205-207 (1865). 



Helix angulata, Rackett, Lin. Tr. xiii. 42, pi. 5, fig. 1 (1822). — Wood, Cat. Suppl. pi. 

 7, fig. 12 ; Hanley's ed. 226. 



Hdix bicarinatus, Eaton, Zool. Text Book, 194 (1826). 



Planorbis engonatus, Conrad, N. Fresh \V. Sh. Suppl. 8, pi. 9, fig. 8 (1834). 

 Lister, 139-144. 



Shell orbicular, its tulie rapidly increasing, deeply excavated on 

 both sides, color brownish yellow on the carina. Whorls rather 



