132 LAND AND FRESH WATER MOLLUSKS 



Genus Margaritana Schumacher. 

 Margaritana margaritifera Linne. 

 Typical form : 



Mya margaritifera LINNE, Syst. Nat., ed. x, p. 671, 1758, Conch. Cab., vi, pi. 



i, fig- 5- 

 Alasmodonta arcuata BARNES, Am. Journ. Sci., vi, p. 277, pi. xn, fig. 20 



1823. 



Unio elongatus LAMARCK, Anim. s. Vert., vi, p. 70, 1819. 

 Unto sinuata C. PFEIFFER, 1825 ; -f U. roissyi Michaud, 1831 ; + U. tristis 



Morelet, 1845 ; + U. crassissimus (Klein) Lea, 1836. 

 Unio (Alasmodonta} dahuricus MIDDENDORFF (1850), Sib. Reise, u, p. 275, 



pi. xxvi, figs. 3-5, 1851. 

 Unio complanatus MIDDENDORFF, Sib. Reise, u, p. 273, pi. xxvn, figs. 1-6, 



1851. 

 Unio mongolicus, MIDDENDORFF, Sib. Reise, n, p. 277, pi. xxvn, figs. 7-8, 



1851. 

 Margaritana margaritifera SIMPSON, Synopsis, pp. 674-677 (ex parte), 1900. 



Margaritana margaritifera variety falcata Gould. 



Alasmodon falcata GOULD, Proc. Boston Soc. N. Hist., in, p. 294, Nov., 

 1850; Wilkes' Expl. Exp. Moll., p. 433, figs. 545, a-b, 1852. 



Unio falcatus SOWERBY, Conch. Icon., xvi, Mon. Unio, pi. LXXV, fig. 390, 

 1868. 



Alasmodon yuba'ensis TRASK, Proc. Calif. Acad. Sci., I, p. 30, 1855. 



Range of the type. The whole of northern Europe and western 

 Siberia. In northeastern Asia from the Upper Amur basin and south- 

 ern Mongolia, Kamchatka, and Sakhalin Island. In America on Anti- 

 costi Island ; Quebec Province, eastern Canada ; New England and 

 New York. Also, isolated from the eastern area by a wide gap, in 

 the Lower Saskatchewan near Lake Winnipeg. 



Range of the variety. California, in the Sierra, Plumas Co., at 

 7,400 feet above the sea ! Sacramento River ; Yuba River ; Oregon ; 

 Washington at Wallawalla ; northwestern Montana in the headwaters 

 of the Missouri ! (only) above Fort Benton, but not reported lower 

 down ; Victoria and Nanaimo ! Vancouver Island ; Fraser River ; 

 Kakwous Lake (4,000 feet elevation) and streams in Lat. 50, Brit- 

 ish Columbia ; Naha Bay, Alaska, abundant near sea level in small 

 lake, Lat. 5535 North ! 



The most obvious distinction between the typical form and variety 

 falcata lies in the purple nacre of the latter, which is often extremely 

 rich and beautiful, though in old cabinet specimens usually much 

 faded. The specimens above the falls in the headwaters of the Mis- 

 souri may have been captured with streams by orographic changes, 

 or transported in the glochidium stage attached to fishes ; at any rate 



