119 
ple, varying in this respect; more reflected and aperture more 
effuse at the columella. Parietal wall in the heavier examples 
calloused, the callous connecting with the inner edges of the outer 
lip above and below. Shelli rather fragile, thin, translucent, sur- 
face smooth and shiny, and sculptured with fine incremental lines. 
color pale horn to white, and otherwise marked by a single narrow 
revolving reddish-brown band just above the periphery, which in 
some specimens is obscure or absent. In some individuals certain 
faint scars upon the upper whorls imply an occasionally hirsute 
character. Max. diam. of largest 15.25, of smallest adult 13.75; 
Min. diam. of largest 13.25, of smallest 12, Alt. of largest 10.25, 
of smallest adult 8.75 mm.’’—Stearns, U. S. Natl mus pr 13:206, 
£P25)f 6-8) 
Type locality:—Grand canyon of the Colorado, opposite Kai- 
bab plateau, at an elevation of 3,500 feet (C. H. Merriam). 
Stearns, Nautilus 8:29 records from Resting Springs, Inyo 
Co., Cal. (Vernon Bailey), and Mountain Springs, San Diego Co., 
Cal. (C. R. Orcutt). 
1635 Mactra (Mactroderma) velota Phil. 1848. 
Gulf of Cal. to Panama. 
1636 Mactra (Mactrotoma) nasuta Gld. 1851. 
Baja Cal. to west Columbia. 
Synonymy: M. californica Desh. (not Conr.).—M. hiantina 
Desh. etc. 
1637 Mactra (Mactrella) exoleta Gray, 1837. 
Gulf of Cal. to Guayaguil. 
1638 Mactra (Mactrella) elegans Sby. 1825. 
Gulf of Cal. to Panama. 
1639 Spisula (Hemimactra) catilliformis Conr. 1867. 
Neeah bay, Wash., to San Diego, Cal. 
Synonymy: Standella californica Cpr. not Conr.—Mactira ¢ca- 
tilliformis Dall. 
1640 Spisula (Hemimactra) Hemphilli Dall. 1894. 
San Diego, Cal. 
1641 Spisula (Hemimactra) planulata Conr. 1837. 
Monterey to San Diego, Cal. 
1642 Spisula (Hemimactra) polymyma Stm. 1860. 
1643 Variety alaskana Dall. 1894. 
Icy Cape to Neeah bay, Wash. 
1644 Mulinia palida Brod. & Sby. 1829. 
Cape San Lucas to Panama. 
1645 Mulinia Gabbi Tryon. 1869. 
cp > pe California. Near M. exalbida Gray, of South America 
all). 
1646 Gnathodon (Rangianella) mendicus Gld. 1851. 
Estuaries, Gulf of California. 
1647  Labiosa anatina Spengler. 1802. West Mexico. 
1648 Tresus Nuttallii Conr. 1837. 
Sitka, Alaska to San Diego, Cal. 
Synonymy: Lutraria maxima Midd. 1849, non Jonas 1844.— 
L. capax Gld. 1850.—L. inflata Dunker, 1853. 
