498 LIMN^ID^. 



Planorhis ehvatus, Adams, Bost. Journ. Nat. Hist. iii. pi. 3, fig. 15. — Gould, In v. 207. 



Shell small, light grass-green, translucent, faintly marked with 

 lines of growth ; whorls three and a half or four, the tube not rap- 

 idly enlarging, and considerably flattened ; whole shell flat, or 

 slightly elevated above, the tip depressed so as to form a small pit ; 

 below forming a deep, tunnel-shaped cavity, the whorls presenting 

 an obscure angle as they revolve around it ; suture deeply im- 

 pressed ; aperture slightly oblique, its upper edge on a level with 

 the spire, or very slightly declining ; lower edge descending consid- 

 erably below the level of the under surface ; portion of the preced- 

 ing whorl embraced by the aperture constituting about one fifth of 

 its circuit. Breadth, one fourth of an inch ; height, one tenth of 

 an inch. 



Inhabits rivulets and pools in Norfolk and Plymouth Counties. 



This shell is closely allied to P. parvus and P. hirsutus. But the 

 first is a more depressed, discoidal shell, its upper surface more 

 broadly and deeply concave, the lower surface very little more con- 

 cave than the up])er, and the aperture much more oblique. P. hir- 

 sutus has a still greater altitude, a very rapidly increasing tube, is 

 deeply concave above and l)elow, its color is lighter, and its lines of 

 hairs, when present, afford a very marked distinction. It may pos- 

 sibly prove to be the immature shell of some other species. 



[As will be seen by the synonymy of the last species, I consider 

 this identical with it. — AV. G. B. 



Planorbis dilatatus. 



Fig. 140. 



Shell small, circumference carinated, flat above, convex below, and with a small, 

 deep umbilicus ; whorls three ; aperture large, expanded. 



Planorhis dilatatus, Gould, Inv. of Mass. 210, fig. 140 (1841) ; Otia, 182. — Haldeman, 

 Men. 2.3, pi. 4, figs. 16-18 (1844). — De Kay, N. Y. Moll. 66 (184.3). — Anon. 

 Can. Nat. ii. 209, fig. (18.57). — W. G. Binney, Smith. Inst. L. and Fr. W. Shells, 

 ii. 131, fig. 218 (186.5). 



Planorhis dilatm, Haldeman, Men. 2.5 (Jan. 1844). 



FiR. 748. ^\-\(i\\ small, of a yellowish-green color, minutely wrinkled 

 ^ by the lines of growth ; spire flat, composed of not more 



^ than three whorls, separated by a Avell-dcfined suture ; the 

 „®^ outer whorl has a sharp margin on a level with the spire, 



«'«. diminishing near, but still modifying, the aperture ; below 

 this line the whorl is very convexly rounded so as to encircle a 



