OF NORTH AMERICA. 87 



B. DESCRIPTIONS OF AMERICAN FOSSIL LYMNyEAS. 

 COMANCHEAN LYMNAEAS. 



Galba ativuncula (White). Plate XVI, figures 1, 2. 



Limnaa ativuncula WHITE, Bull. U. S. Geol. Surv., no. 29, p. 20, pi. 4, 

 figs. 10-11, 1886; Proc. Amer. A. A. Sci., XXXIV, p. 241, 1890; Bull. U. S. 

 Geol. Surv., no. 128, p. 71, 1895. BOYLE, Bull. U. S. Geol. Surv., no. 102, p. 167, 

 1893. SCHUCHERT, Bull. U. S. Nat. Mus., no. 53, i, p. 355, 1905. 



"SHELL small, spire moderately slender; volutions about six in 

 number, convex, the last one enlarged and somewhat longer than the 

 spire. Surface marked by the usual lines of growth. 



"Length of the largest example in the collection, 8 millimeters; 

 but their average length is considerably less" (White). 



TYPE : U. S. Nat. Mus. no. 20054. 



HORIZON : Atlantosaurus beds, Comanchean Period. 



LOCALITY: Eight miles north of Canyon City, Fremont County, 

 Colorado. 



REMARKS : "The younger examples of this species are more slen- 

 der than the adult specimens on account of the proportionally greater 

 enlargement of the last volution upon reaching maturity. These younger 

 examples are so slender as to suggest their reference to Acella, but 

 the older shells have more the shape of true Limnsea" (White). 



From the figures, this species most nearly resembles certain recent 

 Lymnaeas which Lea described as rustica. It certainly falls in the group 

 with obrussa, rustica, plica and parva, and could scarcely be distin- 

 guished from certain individuals of these species had the specimens 

 the fresh appearance of recent shells. Occurring as it does in the 

 oldest strata from which American Lymnaeas have been secured, the 

 parallel in resemblance is all the more remarkable, showing clearly, 

 as remarked by Dr. White, that the Lymnseid fauna was well estab- 

 lished at this period. 1 



Galba consortis (White) . Plate XVI, figures 3, 4. 



Limnaa consortis WHITE, Bull. U. S. Geol. Surv., no. 29, p. 20, pi. 4, figs. 

 8-9, 1886; Bull. U. S. Geol. Surv., no. 128, p. 71, 1895. BOYLE, Bull. U. S. Geol. 

 Surv., no. 102, p. 167, 1893. SCHUCHERT, Bull. U. S. Nat. Mus., 53, i, p. 356, 

 1905. 



"SHELL moderately small; spire short; volutions about five in 

 number, convex, the last one inflated and much longer than the spire. 

 Surface marked by the usual lines of growth. 



"Length of largest example, 10 millimeters; breadth of the last 

 volution, 5 millimeters" (White). 



^Amer. Journ. Sci., iii, vol. XX, p. 44. 



