THE NAUTILUS. 17 



Trout River, Marquette Co., and the St. Mary's River at Saulte 

 Ste. Marie, Mich. 



This variety differs from the usual and more typical form (pi. I, 

 fig. 4 and pi. II, fig. 8) of general distribution in the lower Penin- 

 sula, by its slender, elongated form. It is apparently characteristic 

 of the small rivers tributary to Lake Superior. With the exception 

 of a few specimens from Saulte Ste. Marie, the typical form of 

 desidiosa has not been as yet found in the Upper Peninsula at all. 

 Peninsulse is very similar in shape to a small form of general distri- 

 bution through the State, which is probably referable to some one of 

 Lea's indefinite species, but differs b}'^ its much greater size, being 

 twice as long with the same number of whorls. As a characteristic 

 local form of a large region, it seems worthy of a name. 



Lymnaea davisi n. sp. PI. II, fig. 9-10. 



Shell of medium size, globose-conic ; perforate ; light horn-color ; 

 whorls 5 ; the spire about one-third of the entire length ot the shell, 

 rapidly acuminating and with a minute, sharp apex ; the whorls of 

 the spire are flattened and but slightly convex, with a distinct, but 

 not deeply impressed, suture ; body whorl large, inflated, ovate, 

 flattened above and rounded below ; lines of growtli distinct, fine and 

 regular, minutely decussated with revolving spiral lines ; aperture 

 large, pear-shaped, acutely angled above and broadly rounded below, 

 about three-fifths of the entire length, lip sharp, slightly thickened 

 within, straight above, somewhat expanded below, broadly reflected 

 over and nearly covering the small umbilical perforation ; columella 

 with a very slight fold ; axis rather thick, round, scarcely it' at all 

 folded. 



Alt. (Fig. 9) 15.2, diam. 7.5 mm. 



Alt. (Fig. 10) 15, diam. 7.5 mm. 



Types (No. 20092 coll. Walker) from Fish Point, Tuscola 

 County, Mich. This species is well characterized by its large, ovate 

 body whorl and its very acute spire; the apical whorls are flattened 

 and the straight line of spire is prolonged over the upper part of tiie 

 body, giving a " pot-bellied " appearance to the shell. 



Named in honor of Prof. Charles A. Davis of Ann Arbor, its dis- 

 coverer, in recognition of the many valuable contributions he has 

 made to our knowledge of the distribution of the moUusca in Michi- 

 gan. 



