126 I^AND AND TRESII- WATER SHELLS OF X. A. [PART II. 



Planorbls planulatus, Cooper, Report on the Is'at. Hist., &c., of Wasliing- 

 ton Terr., &o., p. 378 (1859) ; P. R. R. Rep. XII, 378. 



Dr. Gould's description and figures are given above. There 

 can be no doubt of the identity of Cooper's species with it. The 

 Fig. 209 is drawn from a shell furnished by Judge Cooper, who 

 also has enabled me to examine all the shells col- 

 Fig. 209. jgg^g^i Y)y Dr. Cooper. 



Planorbls planulatus, Cooper.— A small carinated specie.?, 

 flat above, convex below, having much the appearance of a 

 I norUs Vahuta, found only in Lakes on Whidby's Island at the 



plaTukiZ. entrance of Puget Sound. ^Cooper.) 



Fig. 210. 



rianorhls 

 t.vacutu-1. 



Planorbls exaciitus, Say.— Dextral, depressed, with an acute 

 edge. Inhabits Lake Champlain. Cabinet of the Academy. 



Shell depressed ; whirls four, striated across, wider than long, not ele- 

 vated above the suture, but a little flattened, sides obliquely descending 

 to an acute .lateral edge, below the middle ; spire not im- 

 pressed ; sutiire not profoundly indented ; beneath, body whirl 

 flattened, on the inner edge rounded ; umbilicus regular, ex- 

 hibiting all the volutions to the apex; aperture transversely 

 sub-triangular; labrum angulated in the middle, arcuated 

 near its hiferior tip, the superior termination just including 

 the acute edge of the penultimate whirl. Greatest breadth 

 rather less than I of an inch. 



This species was found in Lake Champlain by Mr. Augustus Jessup, who 

 deposited it in the collection of the Academy. Only two specimens occurred. 

 It may be readily distinguished from P. parvus, by its more convex form 

 above the spire not being impressed, and by its very acute lateral edge. 

 It appears to be prettv closely allied to Planorbls nitidus of Europe, but it 

 is larger, the umbilicus much more dilated, and the aperture does not 

 embrace the penviltimate whirl so profoundly. {Say.) 



Planorbls exacuUis,SKX,Jour. Acad. Nat. Sc. II, 1G5 (1821): Bixkev's 

 ed. 64.-HALDEMAN, Mon. 21, pi. iv, f. 1-3 (1844). -Gould, Inv. 

 of Mass. 208, f. 137 {1841).-Adams, Shells of Vt. 155 (1842).- 

 DeKay, N. Y. Moll. 63, pi. Iv, f. 62 a, b (1843). -Anon. Can. ^at. 

 II, 207. fis. (IS."). 

 Planorbls lens, Lea, Tr. Am. Phil. Soc. VI, CS, pi. xxiii, f. 83; Obs. II, 



68 (1839). * 



