THE NAUTILUS. 87 
a. Depressed ; periphery with a strong, cord-like keel ; back 
of body whorl gibbous below suture; umbilical area mod- 
erate or large, bounded by a keel. Alt. 5-2, diam. 6 mm. 
P. RUSHII n. sp. 
aa. Globose, without keels; periphery rounded ; no ridge or 
hump on the back; umbilical area small, with angular 
edge; yellowish or olivaceous-brown, unicolored or with 
subsutural and superperipheral green bands. Alt. 5, diam. 
54 mm. P. IHERINGI 0. sp. 
II. No groove on face of the columella. 
a. With 5 or 6 spiral keels, all, or the upper two with acute 
tubercles ; operculum with several whorls. Alt. 8-9, diam. 
10 mm. P. MULTICARINATUS Mill. 
aa. Shell carinated or angulate, without tubercles. 
b. Peripheral keel visible on the penultimate as well as 
the last whorl; lip expanded or varixed. 
c. Trochoidal, with acutely, straightly conic spire, 
compressed median peripheral keel, a small sub- 
sutural carina, and a basal keel defining a very 
Jarge umbilical tract. Aperture much contracted, 
the lip varix very high, recurved above periphery, 
the highest point of recurved lobe connected with 
lip-edge by a short oblique rib. Alt. 5:2, diam. 
6 mm. P. MICROTHAUMA D. sp. 
ce. Trochoidal, with high conic spire and flattened 
base and acute peripheral keel; surface smooth 
above and below the keel, whorls flat above, the base 
slightly convex ; umbilical area very narrow, in- 
conspicuous ; lip varix narrow, near the lip edge. 
Alt. 5, diam. 5 mm. P. HIDALGOI n. sp. 
cec. Elevated turbinate, with an acute peripheral 
keel, convex above and below it; lip expanded. 
Alt. 5, diam. 5 mm. P. PERISTOMATUS Orb. 
bb. Peripheral keel or angle concealed on the penultimate 
whorl. 
ce. Lip varix very strong, recurved above ; periphery 
hardly angular, base convex, back of body whorl 
with a spiral rib below the suture ; aperture much 
contracted ; no columellar area defined. Alt. 5, 
diam. 53 mm. P. DINOCHILUS ND. sp. 
