THE NAUTILUS. 63 
P, glaphyrus var. between polygonatus andimmanis. (PI. II], figs. 5, 6.) 
The two specimens figured are of the same size but differ in sculpt- 
ure. One (fig. 6) is smooth above and below, having a strong sub- 
spinous keel at the periphery, and a smooth, acute keel below it. 
Upon the earlier whorls of the spire there are longitudinal waves, 
and two spiral cords above the peripheral keel, which diminishes 
in size. The base has no spirals. The other specimen has the 
entire body-whorl spirally lirate (lire on body-whorl 9, on penullti- 
mate whorl 3) and strongly plicate. 
P. glaphyrus potamarchus. (PI. III, fig. 7.) 
This is one of the largest. forms of Pachychilus known, and it is 
the most aberrant of the glaphyrus stock. The shell is rather 
slender and acutely conical, the outline of the spire being straight. 
The aperture is ovate, narrowed above, and one-third the length of 
the shell. Whorls 10-11 remaining, several of the earlier being 
lost by erosion. The microscopic sculpture is the same as in var. 
Rovirosai. There are no traces whatever of the waves or folds so 
prominently shown by the other varieties of glaphyrus, and the 
spiral cords are also completely obsolete, or indicated by the faintest 
traces on the base. The color is olive-green or olive-brown. 
Alt. 99, diam. 33 mill. 
Alt. 87, diam. 29 mil. 
Tabasco, Mexico. 
This variety differs from the pyramidalis of Morelet in being 
larger and smoother, lacking altogether the chestnut colored spirals 
of that form. 
Potamanax subgen. nov. 
Shell solid, oval with short conic spire, spirally sculptured or 
banded. Aperture ovate, acute above, broadly rounded below ; 
outer lip not sinuous; inner lip more or less heavily calloused, not 
notched at the base. Operculum few-whorled, with basal nucleus. 
Type P. Rovirosai Pils. 
This group has the sculpture of Hemisinus but differs from that 
genus in the entire, un-notched basal lip. The columella callus is 
much like some species of Pachychilus but the operculum is very 
different from that genus. From both of these groups it differs in 
the short, ovate contour of the shell. The description of the oper- 
culum is taken from Melania brevis d’Orbigny of Cuba, which 1] 
consider congeneric. 
The relationship of Potamanax to Hemisinus in sculpture and 
operculum is obvious, and has caused me to regard it as an subgenus 
