HAN>-IBAL : CALIFOK.XIAX FKKSHWATZE MOLLUSCA. 125 



American species. Attempts a hundred years or more later to 

 establish cygnea as the type of Anodontites are post mortem. 



The Simpsonian Anudonta included a varied assortment of edentate 

 Anodontinte such as iinbeciUis, grand is, rnargmata, dejecta, and 

 stiborbiciilata, derived withoiit doubt from several none too closeh* 

 related stocks possessing hinge-teeth. Since the resemblances are due 

 chiefly to parallel modifications, these can hardly be regarded as 

 congeneric with A. cggnea, which is the only true Anodonta, in America 

 at least. The proper segregation of these species which lack the most 

 important index to their relationships is hardly a simple problem. 

 The anatomy, of prime import in the discrimination of more com- 

 prehensive groups, ofFers only partial aid, and other characters, such 

 as the adolescent stages and beak sculpture, should enter into con- 

 sideration. A too conservative use of the latter character cannot be 

 recommended, however ; the development of plications, pustules, etc., 

 is subject to considerable individual and colonial variation in species 

 which have not entirely passed beyond the sculptured stage, and it is 

 reasonable to suppose that this variation remains latent, thougli the 

 sculpturing is carried back to the earliest post-glochidial growth. 

 Anyone may satisfy himself of the truth of this by examining a large 

 series of Anodonta cygnea from random localities. 



AxoDOXTA CTGXEA (Linne). PI. Y, Figs. 3, 4, 8. 



Mytilus cygneus, Linne, 1758 ; 21. anatinus, Linne, 1758 (svntonic 

 form) ; A. CeUensis, C. Pfeiffer, 1821 ; A. ponderosa, C. Pfeiffer, 

 1825 (syntonic form); A. Oregonensis, Lea, 1836; Anodon 

 cognata, Gould, 1850; A. Kennerlyi, Lea, 1861. 



AxoDOXTA CYGNEA i:MPrKA (Say). PL Y, Figs. 1, 2, 7. 



A. impura, Say, 1829 ; A. NuttaUiana, Lea, 1838 ; A. Wahlainatensis, 

 Lea, 1838 (syntonic form); A. coarctata, Anton, 1839 (syntonic 

 form); A. Califor7uensis,\jea, \8b'2; A. triangularis, '^lask, ISoo 

 (syntonic form) ; A. rotnndovata, Trask, 1855 (syntonic form) ; 

 A. exilior, Lea, 1871 (syntonic form) ; A. Xidtalliana, var. 

 Idahoensis, Hemphill, 1891 (syntonic form); A. Chapalensis, 

 Crosse & Fischer, 1892 (syntonic form); A. Chalcoensis, Crosse 

 and Fischer, 1893 (syntonic form); A. {Kuttalliana var.?) 

 lignitica, J. G. Cooper, 1894; A. Xetikmanensis, Arnold, 1910 

 (syntonic form). 



AxoDoxTA CYGNEA Beringiana (ILiddeudorf). PI. Y, Figs. 5, 6. 



A. Zellensis, var. Beringiana, Middendorf, 1851 ; A. Youconensis, 

 Lea, 1867; A. Youlcanensis, Lea, 1868. 



Anodonta cygnea impura. Shell of moderate size, quadrate-discoidal, 

 alate, decidedly broader posteriorly, rather compressed, early growth 

 similar in outline to adult; habitat sluggish streams and lakes. 



Western and mountainous portions of ^lexican Province from tlie 

 vicinity of llexico City northward. Arizona, Los Angeles, Mojave, 

 Colorado, Coast Range, Klamath, Xevada, Utah, and Columbia 

 Systems, rarely farther north. 



