PLANORBIS. 491 



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

 sluggish. 



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



pools. 



This is a somewhat darker shell than P. tricolvis, 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. trivolvis, the 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. lentils or a new species. 



[Professor Haldeman refers it to P. trivolvis, var. fallcix. In the 

 "Land and Fresh- Water Shells," Part I., 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 preceding whorl. 



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

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

 Moll. An. pi. 310, fig. 1. — Haldemax, Mon. vii. 6, pi. 1, fi<j;s. 1-6 (1844). — Ad- 

 ams, Shells of Vt. 155 (1842). -De Kay, N. Y. Moll. 60, pi. 4, fig. 63 (1843).— 

 Gould, Inv. of Mass. 203, fig. 134 (1841). — Chemn. 2d. ed. 56, pi. 60, fio-s. 11-13. 

 — PoTiEZ et MiCHAUD, Gal. des Moll. i. 207, pi. 21, fiL^s. 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 anguluta, Rackett, Lin. Tr. xiii. 42, pi. 5, fig. 1 (1822). — WoOD, Cat. Suppl. pi. 

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



Helix Idmrinatus, Eaton, Zool. Text Book, 194 (1826). 



Planorhis engonatus, Conrad, N. Fresh VV. Sh. Suppl. 8, pi. 9, fig. 8 (1834). 

 Lister, 139-144. 



Shell orbicular, its tube rapidly increasing, deeply excavated on 

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



