THE NATURAL HISTORY SURVEY. 251 



Geological distribution: Pleistocene; Loess of North Amer- 

 ica, Europe and Asia. 



Habitat: Found plentifully under wood, leaves, stones, 

 old logs, in moss and on the banks of streams. Gregarious. 



Remarks: This is our most common Vallonia^ and cannot 

 be confounded with any other in this region, where the shell 

 always has a transparent or translucent horn color. The aper- 

 ture and deflection of the last whorl varies to some extent, 

 but with all this variation it is a species which will be at once 

 recognized when seen. It is frequently found on flower-pots in 

 Chicago residences, and is the most widely distributed species 

 of the genus, being found in each of the three regions. It has 

 been found in large numbers west of the poor farm at Dunning 

 under board walks. 

 100. V'allonia costata Miiller, 



Helix costata MULLER. Verm. Hist., Vol. II, p. 81, 1774. - 



Vallonia rosalia, 1826 (ex. WESTERLUND, Fauna, Vol. I, p. 14). 



Vallonia costata var. helvetica STERKI, Proc. Phil. Acad., p. 262, 1893. 



Vallonia costata var. amurensis STERKI, 1. c. 



Vallonia costata var. pyrenaica STERKI, 1. c. 



Vallonia costata var. montana STERKI, 1. c., p. 263. 



Shell: Small, depressed convex, rather solid, umbilicated; 

 surface shining, with regular membranous ribs of good size, 

 the intercostate spaces being finely striate; color reddish- 

 horn; periphery a trifle angled; sutures deeply impressed; 

 whorls three and one-half, rapidly increasing, the last expand- 

 ing and descending, somewhat angular on the periphery; spire 

 flat, apex finely striate; aperture nearly circular, a little ob- 

 lique, flattened above, angular below; peristome reflected, 

 white, terminations approaching and connected by a thin 

 callus; umbilicus open, large, spreading, exhibiting all the vo- 

 lutions. 

 Greater diameter, 2.70; lesser, 2.25; height, 1.30; umbilicus, 0.85 mill. 



Animal: Similar to pulchella. 



Jaw: Similar to that of pulchella, ribs sixteen to eighteen, 

 ends of jaw smooth, cutting edge denticulated. 



Radula formula: ^+i+|+i+|+i+A (13-1-13); 

 central tooth as in pidchella; the side cusps very small; laterals 

 with a long, thin inner cusp and a very small outer cusp, with 

 cutting points as in pulchella; transition teeth (five) with the 

 outer cusps split; the first marginals have but three cusps, but 



