96 LAND AND FRESH WATER MOLLUSKS 



Planorbis (Torquis) nathorsti Westerlund. 



Planorbis nathorsti " Westerlund, Vega Expd., iv, p. 168, 1887. — Posselt, 

 Consp. Fauna Gronl. Moll., p. 162, 1898. 



Aulatsivik, West Greenland (Sofia Expedition) ; Labrador (Storer). 



This species is said to approach P. arcticus, but has four and a 

 half turns in a diameter of 3.5 mm., while the latter turns only three 

 and a half times in 5.0 mm. P. nathorsti has spiral as well as trans- 

 verse striation. It has not been figured. 



Some specimens in the National Museum collected in Labrador ex- 

 hibit about four turns in 3.5 mm. diameter, according to my calcula- 

 tion, but so much personal equation enters into the estimation of the 

 extent of the first whorl that I am inclined to think they belong to 

 Westerlund's species, in which case it is intermediate between parvus 

 and arcticus, but without the excavated umbilicus of the former. 



Planorbis (Torquis) arcticus Moller. 



Planorbis arcticus (Beck, MS.) Moller, Index Moll. Gronl., p. 5, 1842.— 

 Morch, Am. Journ. Conch., iv, p. 32, pi. iv, fig. 9, 1868. — Morch, in 

 Rink's Danish Greenland, p. 436, 1877. 



Range. — West Greenland ! Fort Chimo, Ungava, Labrador ! 

 Species with larger whorls, the last more expanded near the aper- 

 ture, and with the sides of the umbilicus not excavated as in P. parvus 



Say. 



Planorbis (Torquis) umbilicatellus Cockerell. 



Planorbis umbilicatus Taylor, Journ. Conch., iv, p. 351, 1885 ; not of Mid- 

 ler, 1774. Manitoba. 



Planorbis umbilicatellus Cockerell, Conch. Exch., 11, p. 68, Nov., 1887. — 

 Vanatta, Nautilus, ix, No. 10, p. 117, 1896. 



Range. — From Mesilla, New Mexico! northward, through Col- 

 orado, Montana, Iowa, Minnesota, to Manitoba. 



Rapid City, Birtle, Brandon ! in Manitoba ; McLeod, Red Deer, 

 Olds, Laggan, in Alberta. 



Planorbis (Armiger) crista Linne. 



Nautilus crista Linne, Syst. Nat., ed. x, p. 709, 1758. 

 Turbo nautilcus Linne, Syst. Nat., ed. xn, p. 1241, 1767. 

 Planorbis imbricatus Muller, Hist. Verm. Terr., n, p. 165, 1774- 

 Planorbis cristatus Draparnaud, Hist., p. 44, pi. II, figs. 1-3, 1805. 

 Planorbis nautileus Gray, Turton's Man. Land and Fw. Shells, p. 236, pi. 



vm, fig. 94, 1857. 

 Planorbis costatus De Tar and Beecher, leaflet of one page, Albany, Oct. 



25, 1878. 

 Planorbis crista Woodward, Brit. Nonmarine Moll., in Journ. Conch., x, p. 



355- I9°3- 



