122 PKOCEEDINGS OF THE MALACOLOGICAL SOCIETY. 



MaRGAKITANA MARGAEITIFEKA FALCATA (Goulcl). 



Alasmodonta falcata, Gould, 1850 (syntonic form, hardly typical); 

 Alasmodon Yubaensis, Trask, 1855. 



If. margaritifera. Shell of moderate size, elongate-elliptical, umbones 

 rather low, lateral teeth sub-obsolete in normal adult, nacre usually 

 bluish or pinkish ; habitat rapid streams. 



Boreal portion of Palaearctic and Atlantic seabord of Nearctic 

 regions, infrequently v>ith. falcata in Califoruian Province. 



2f. margaritifera falcata. Shell similar to margaritifera, but the 

 lateral teeth totally obsolete, pseudo-cardinals much reduced, nacre 

 prevailingly lurid purple or orange; margaritifera stage completed 

 before mid-adolescence ; habitat similar. 



American Province in upper Missouri River. Fraser, Columbia, 

 Klamath, Utah, j!^evada, and Coast Range Systems. 



Quaternary : Bonneville Lake beds, Utah ; Lahoutau Lake beds, 

 Nevada. 



The distribution of this species has been made the subject of an 

 interesting paper by Walker.' The supposed Eocene record is the 

 3Iargaritana ITerrei, but the poorly preserved material then at hand 

 from Tesla, California, showed no lateral teeth. It is probable that 

 M. margaritifera falcata at no point extends south of the latitude of 

 Monterey Bay, California. 



The very young of this mollusc were once obtained, with Splmriiim, 

 in a little spring under the bank of a brook in which the adults were 

 common. 



Unrecognized: '■ TJnio [Margaritanay onariotis, Mayer, 1869. 

 Miocene (?) of Alaska. 



Family U^N'IONID^, Swainson, 1840. 



Shell of moderate size, unioniform, margaritanifurm, or anodonti- 

 form ; animal as described above ; glochidium spadiform, each valve 

 armed with a spine ; habitat fluviatile and lacustrine. 



Sub-family UMONII^^, s.s. 



Shell of moderate size, unioniform or margaritaniform ; animal as 

 described above, taehylictic (?) ; habitat fluviatile and lacustrine. 

 Genera : Unio, JJigrafiaJa. 



Sub-family ANODONTIN^, Swainson, 1840. 



Shell of moderate size, thin or sub-solid, unioniform, margaritani- 

 form, or anodontiform ; animal as described above, brachylictic ; 

 habitat lakes and streams. 



Genera : Anodonta, Gonidea, Arnoldina. 



The recognition of two Unionidoe, unquestionably congeneric with 

 living European species, in the Eocene-Oligocene of the Pacific Coast, 

 throws interesting light upon the former ranges of these genera, not 

 to mention the evidence afforded of their considerable antiquity and 

 the fixity of their characters. 



1 Proc. Make. Soc. Lond., ix, pp. 126-45, 1910. 



