﻿ANODONTA 



385 



ways rounded ; dorsal wing- low, subangular behind ; posterior 

 slope truncate; surface with irregular growth lines, which 

 sometimes form ridges ; epidermis pale olive-green or dirty 

 brownish, sometimes banded and faintly rayed, somewhat 

 shining; nacre dull whitish or bluish, usually lurid purple in 

 the cavity ; hinge sometimes thickened and showing faint ves- 

 tiges of teeth. 



Length 85, height 48, diam. 27 mm. 

 Length 84, height 44, diam. 2^ mm. 



Arizona?; southeastern California; northwest Mexico. 

 Anodonta dejecta Lewis, Field and Forest, I (August and 

 September), 1875, f). 26; Yarrow's Report, 1875, p. 952.— 

 Simpson^ Pr. U. S. Nat. Mus., XIX, 1896, p. ^72, pi. xxxii, 

 figs- 4, 5 ; Syn., 1900, p. 630. 

 Anodonta mearnsiana Simpson, Nautilus, VL 1893, p. 134. 

 Arnoldina dejecta Hannibal, Proc. Mai. Soc. London, X, 

 I912, p. 129, pi. VI, fig. 9. 



This species approaches A. calif orniensis on the one hand 

 and forms of Con idea angnlata on the other. It is generally 

 larger and always heavier than the former as well as more 

 rhomboid and brilliant. It never has the sharp posterior ridge 

 of the latter, nor its incipient teeth. I have examined many 

 specimens of the animal but have never seen one gravid. 



It is said to be from Arkansas River or its tributaries west 

 of the one hundredth meridian and collected by Dr. H. C. 

 Yarrow, surgeon and naturalist of Wheeler's expedition. This 

 locality is erroneous, as it belongs, no doubt, exclusively to the 

 Pacific drainage. 



Hannibal, (1. c. p. 128), makes this species the type of a 

 new genus, Arnoldina, based on "the development, peculiar 

 beak sculpture and an indescribable velvetv texture of the 

 shell." 



Group of Anodonta cataracta. 



Shell thin or solid. iuHated, rather evenly rounded in front, 

 generally somewhat biangulate behind and very slightly winged 

 in the post-dorsal region; beaks rather full, the sculpture con- 

 sisting of a moderate number of concentric ridges or corruga- 



