7O LAND AND FRESH WATER MOLLUSKS 



which Tryon himself at one time confounded it. It has a short spire 

 with appressed or moderately conspicuous suture, ovate form, tumid 

 whorls, pale color, well marked umbilicus, and fine spiral striation. 

 The largest specimen I have seen measured 27 mm. high and 18 mm. 

 in maximum diameter ; but the average adult is about 24 x 15 mm. I 

 have not seen any specimens angulated at the shoulder. 



Lymnaea (binneyi var. ?) preblei Dall, nov. Plate i, figs, i, 2. 



A shell which when young is almost identical with L. binneyi, and 

 which may prove merely a giant growth of it, occurs in the Hudson 

 Bay drainage. When full grown it has six whorls, with much the 

 same contour as Bulimnea megasoma, the last whorl being much the 

 largest, moderately expanded, and somewhat produced in front. The 

 umbilicus is deep and partly hidden by the reflected pillar lip, which 

 is continuous and more or less raised across the body. There is no 

 fold on the pillar. The surface, when in perfect condition, is minutely 

 but sharply sagrinate by the intersection of axial and spiral striae, and 

 is often malleate besides. The shell is nearly white or pale straw 

 color. 



Adults measure : 



Whorls. Height. Max. Diam. Height of aperture. Diain. 



6 37 23 22.5 13 mm. 



5-5 38 26 26 19 " 



Range. English River, Manitoba (Kennicott) ! Knee Lake, Kee- 

 watin (E. A. Preble) ! 



This form is remarkable for its size, its surface, and its deep umbil- 

 icus. The resemblance of its profile to that of L. megasoma is so 

 marked that one wonders whether some of the records of the latter spe- 

 cies from high northern localities may not have been 

 based on specimens of this form. They are easily 

 separated, however, if one pays attention to the other 

 characters, and the present form probably never at- 

 tains the solidity and rich coloration so characteristic 

 of megasoma. 



FIG. 47. Lym- Lymnaea (Radix?) columella Say. 

 ncta columella. Lymnaa columella SAY, Journ. Acad. Nat. Sci. Phila., i, p. 



14, 1817. 



Lymnceus columellus SAY, Journ. Acad. Nat. Sci. Phila., n, p. 167, 1821. 

 Limnea columella HALDEMAN, Mon. Limn., p. 38, pi. xn, figs. 13-15, 1842. 

 BINNEY, Land and Fw. Sh. N. Am., n, p. 32 (ex parte), fig. 38, 1865. 



