FAMILY LYMN^SID^E 



95 



although they have been called ' characteristic ' by the very authors 

 whose evidence shows the inconstancy. 



Planorbis (Torquis) parvus Say. 



Planorbis parvus SAY, Nicholson's Enc. , 1st ed., II (no pagination), pi. I, fig. 



5, 1817. HALDEMAN, Mon. Limn., p. 27, pi. iv, figs. 19-23, 1844 



(Delaware R.) BIXNEY, Land and Fw. Sh. N. Am., n, p. 133, figs. 222- 



223 (not 224), 1865. 



Planorbis concavus ANTHONY, MS., various catalogues. 

 Planorbis elevatus C. B. ADAMS, Bost. Journ. N. Hist., Ill, p. 327, pi. in, fig. 



1 6, 1840 ; young shell (S. Boston). 

 Planorbis billingsi LEA, 1866, from types (Ottawa, Canada). 



Range. In America, the whole of eastern North America from 

 Florida to N. Lat. 67, and the Yukon drainage system. 



Ottawa, Canada ! northward and westward to Lake Winnipeg ! the 

 Saskatchewan River ! Alberta at Laggan, Olds and McLeod ; Mani- 

 toba at Brandon and Birtle ! Methy Lake ; Moose Factory ! Fort 

 Simpson, Mackenzie River ! Lake Bennett, Yukon Territory ! Left 

 bank of the Yukon below Fort Yukon, Alaska ! 



The most striking characteristic of this widespread species is its 

 'reamed out' umbilicus. P. limophilus Westerlund, its nearest 

 European analogue, may be distinguished at once by its shallow and 

 flattish umbilicus. It rarely shows any trace of spiral sculpture and, 

 when clean, is brightly polished. In the last whorl of 

 the adult the portion above the periphery is usually 

 somewhat flattened or obliquely depressed. 



Planorbis (Torquis) vermicularis Gould. 



Planorbis vermicularis GOULD, Proc. Boston Soc. N. Hist., 

 II, p. 212, 1847 ; Moll. U. S. Expl. Exp., p. 112, pi., 

 figs. 131, a-b, 1852 (Oregon). 



Range. Northern California ! Oregon ! and Van- 

 couver Island, British Columbia ! 



On comparison, the type of P. vermicularis is seen 

 to have vertically deeper whorls than a specimen of P. 

 parvus of the same number and diameter. The aper- 

 ture is more expanded, and much larger, as one 

 would expect from the greater lumen of the whorl. 

 Specimens from middle and southern California have 

 a different aspect and may prove on more careful study to belong to P. 

 parvus. They certainly do not agree with the Oregon shell, which, 

 however, I have seen from Noyo, California. 



FIG. 75. Plan- 

 orbis vermicu- 

 laris Gld. (mag- 

 nified). 



