LYMN^EID^E OF NORTH AMERICA. 373 



the whorls very convex (pi. XXXIX, fig. 13). The Alaska speci- 

 mens do not differ materially from those collected in Greenland. 



Galba vahlii was first mentioned by Beck in his index, but was 

 not described. Moller described it in his index and Morch both de- 

 scribed and figured it in American Journal of Conchology, Volume 

 IV. Authentic specimens received from Morch have been examined 

 both in the Academy of Natural Sciences of Philadelphia and in the 

 Smithsonian Institution. These compare favorably with the speci- 

 mens described and figured in this monograph. 



It has not been possible to successfully differentiate the varieties 

 indicated by Morch in his review of the Greenland fresh-water mol- 

 lusks, in the American Journal of Conchology. All seem to be minor 

 variations of one type of shell. Variety leucostoma is said by Morch 

 (Amer. Journ. Conch., p. 34) to be "somewhat smaller and broader 

 than the type, but differs chiefly by a thick layer of milk-white chalk, 

 which covers all the inside and columella, giving the exterior of the 

 shell a light straw color." This last character is not constant in any 

 large series, besides being a physiologic character. The form minor 

 of this variety (1. c., p. 34) is also a very trivial variation not worthy 

 of a distinct name. The shell of vahlii is seen to vary from short to 

 long spired when a number of specimens are examined. Varieties 

 parva and nitens appear to be local mutations of vahlii as do also 

 wormskioldi Beck and malleata Morch. 



An examination of the axis of vahlii shows it to be placate and 

 a member of the Stagnicola group instead of the Galba group, as in- 

 dicated by Dr. Dall. 



Galba vahlii arctica (Lea). Plate XXXIX, figures 19-23. 



Lymnaa arctica LEA, Proc. Phil. Acad., p. 113, 1864; Journ. Phil. Acad., 

 VI, p. 160, pi. 24, fig. 75, 1866; Obs., XI, p. 116, pi. 24, fig. 75, 1867. SCUDDER, 

 Bull. Nat. Mus., 23, pp. 147, 200, 1885. 



Limnaa arctica TRYON, Con. Hald. Mon., p. 100 (74), pi. 17, fig. 9, 1872. 



Limnophysa arctica TRYON, Amer. Journ. Conch., I, p. 255, 1865. 



Limncea vahlii WHITEAVES, Nautilus, XIX, p. 4, 1905; Ottawa Nat., XIX, 

 p. 66, 1905. 



SHELL : Thick and solid, opaque, oblong-ovate ; periostracum dark 

 horn or chestnut, sculpture as in vahlii; many of the specimens ex- 

 amined have a rather thick epidermis which hides the sculpture of the 

 shell; whorls 5^, convex, rather rapidly increasing in size; sutures 

 well marked but not deeply impressed ; spire short, acutely pyramidal> 

 about as long as the aperture; the spire whorls are inclined to be 

 shouldered, and the fourth and fifth whorls are disproportionately 

 enlarged ; aperture ovate, dark colored within ; outer lip thickened near 



s 



