THE NAUTILUS. 39 
0. undatus W. G. B., Manual of N. A. Land Shells, p. 440, fig. 
483. 
Von Martens has recently expressed the opinion that “ Pilsbry’s 
0. melanocheilus var. floridensis is probably a dark-mouthed variety 
of 0. undatus;'’ but he had not seen a Florida specimen. The 
fact is that this is one of the most distinct forms of the typical 
group of Orthalicus, and if it be a variety of undatus, then undatus 
will cover all of the typical group of so-called species admitted by 
Crosse and Fischer, v. Martens, eh al. 
II. SYNOPSIS OF THE MACTRIDiE OF NORTHWEST AMERICA, SOUTH 
TO PANAMA. 
BY WM. H. BALL. 
Subfamily Mactrin^e. 
Genus MACTRA (Linne) Lam., 1799. 
Subgenus Mactroderma Dali, 1894. 
Shell as in Mactra but rude, inequilateral, with a coarse epidermis, 
pronounced pedal gape, the ligament set off from the cartilage but 
mostly sunken, concentrated dental armature, and the anterior 
arm of the right cardinal in the place of the adjacent ventral lami¬ 
na. Type : 
Mactra (Mactroderma) velata Phil., 1848. Panama to the Gulf of California. 
Subgenus Mactrotoma Dali, 1894. 
Section Mactrotoma ss. 
Accessory lamellae coalescent with laterals and cardinals. 
Mactra (Mactrotoma) nasuta Gould, 1S51. West Columbia to Lower California. 
=M. culifornica Desh., 1854, not Conr., 1837 ; -f M. hiantina 
Desh., 1854 ; -\-M. ovalina Auct. not Lam.; -) -M.falcata Weiukauff 
not Gould; -\~M. fragilis Cpr., 1858, not Gmel. ; -j -M. Deshayesii 
Conr., 1868 ; -\-Merope sp. Weiukauff and Spisula sp. Conrad. 
