170 THE CHICAGO ACADEMY OF SCIENCES. 



emptying into the Atlantic Ocean. Its northward extension to Lake 

 Winnipeg is easily accounted for by the glacial Lake Agassiz and the 

 Pleistocene connection of the Red River of the North with the Minne- 

 sota River. Columella extends throughout the humid divisions of the 

 Lower Austral, Upper Austral and Transition life zones and just over 

 the border of the Canadian zone. 



GEOLOGICAL RANGE : Pleistocene. Goat Island Gravel Pits, Niag- 

 ara River, N. Y. (Letson). This was the only record found referring 

 to the geological range of columclla. 



ECOLOGY : Columella is an inhabitant of ponds and streams where 

 the water is more or less stagnant; a locality with an abundance of 

 lily pads is particularly favorable; it is found also along the shore in 

 shallow water in the vicinity of cat-tails (Typha) and other reeds, 

 upon which it is often found, mimicking the situs of the pulmonate 

 genus Succinea. Rarely found in running water. Columella is a lover 

 of shallow bays and small ponds or creeks, where it may browse in 

 the pond scum and on bits of rotting sterns of water plants. It has 

 been collected by the writer associated with Lymncea stagnalis appressa, 

 Galba obrussa and Galba palustris. Brook flowing from Crawford's 

 into seven-tree pond (Lermond, Maine). 



The following note is interesting, as it illustrates another of the 

 almost unaccountable instances of distribution : 



"The L. macrostoma which I send you requires a note. It comes 

 as near a case of spontaneous generation as anything within my ob- 

 servation. It was found in a little pool about twenty feet in diameter, 

 entirely cut off from streams and fed by a spring. I had for years 

 frequented it for desmidia, etc., in which it was very rich. One season, 

 and one only, appeared these Limncea, which do not occur elsewhere, 

 as far as I now know, within twenty miles. The pond dried up that 

 season and destroyed the locality." (Dr. T. R. Ingalls in Binney, 

 p. 37.) 



REMARKS: Columella may easily be known by its Succinea-like 

 shell, resembling very closely specimens of Succinea ovalis Say. It is 

 subject to considerable variation, especially in the height of the spire 

 and in the size of the aperture; the whorls also vary in convexity. 

 There is also some variation in consistency, some shells being heavy 

 and thick, with a rather rough surface, while others are very thin, 

 delicate and shining. The species is so unlike the other Lymnaeas, 

 however, that it need never be confounded with any species. 



A form (pi. XXIV, figs. 1-3) occurs in the southern states which 

 is considerably smaller than typical columclla, averaging about two- 



