THK NAUTILUS. 77. 



IV. Ancylus parallelus Hahl. (1841). PI. 5, figs. 1-9. 



This common and well-known species has a wide range through' 

 the northern states and Canada, extending from Nova Scotia and 

 New England to Manitoba and Minnesota. It is peculiarly a north- 

 ern form, and its range toward the fouth is comparatively limited, 

 Rhode Island, Central New York, Northern Ohio and Indiana, so 

 far as the records go, seem to mark the limit. It is not listed from 

 Philadelphia (Shick) nor Alleghany Co., Pa. (Stupakopf), nor 

 Cincinnati (Harper and Wetherby), nor the Chicago Area (Baker). 



Mr. Marsh has kindly permitted me to examine the specimens 

 from Mercer Co., III., w.iich he quoted as this species in the 

 NAUTILUS III, p. 34, and they prove to be a form of A. tardus. 

 Shimek's citation from Iowa City, la., which should be verified, if 

 correct, probably marks its extreme range to the southwest, as it 

 does not occur in any of the Iowa lists nor in those of Missouri, 

 Nebraska or Kansas. The tentative citation of this species from 

 North Park. Col., by Ingersoll (Rep. U. S. G. & G. Surv., 1874, 

 p. 405) must also be considered very doubtful. 



It is easily distinguished by its narrow, elongated shell, with 

 nearly straight lateral margins, which widen more or less anteriorly. 

 The anterior slope is typically (fig. 1) only slightly convex, but there 

 is considerable variation in this particular ; the posterior slope is 

 long, very oblique and nearly straight, the right slope is nearly 

 straight, and the left slope slightly convex. The apex is sub-acute 

 and slightly turned towards the right, and is nearly in the centre of 

 the shell. Lines of growth well marked, but fine and irregular. It 

 is at times subject to considerable irregularity in growth, when living 

 on a small reed, the peritreme is concave at the ends (as noticed in 

 A. juscus} and the lateral slopes are noticeably more convex and the 

 apex less prominent. Several examples have been noticed, in which 

 the shell in the earlier stages was unusually narrow, but on ap- 

 proaching maturity, a sudden expansion of the entire margin took 

 place, resolving the peritreme to nearly its normal outline (fig. 4). 

 Specimens of extraordinary size (fig. 7), far surpassing those from 

 any other locality, have been collected by Nylander at Caribou, Me. 

 Specimens nearly as large (7.5 x 4.5 x 3) have been collected by 

 Ferriss on the north shore of Lake Superior. Fine specimens 

 larger than the average also occurred in Schuyler's and Little Lakes, 

 N. Y. (fig. 4). In most places, however, the average length is less 



