MURICID@&. 105 
and Phyllonotus and Chicoreus have the same general facies, 
although they differ in the number of varices. Owing to their 
inter-relationships, no attempt to present the groups in succes- 
sion can be other than exceedingly artificial. 
a. Operculum with subapical nucleus. 
* Varices three. 
MUREX (typical). Shell spinous; spire elevated ; canal very 
long, narrow, nearly straight. 
PTERONOTUS, Swainson. Shell triangular; varices fin-like or 
foliated ; canal moderate, closed, somewhat curved. MM. trigon- 
ulus, Lam. (xliii, 2). 
cuicorEus, Montf. Shell ovate-pyriform; varices foliated and 
sometimes spinose; canal short, curved, wide, nearly closed. MM. 
adustus, Lam. (xliii, 3). 
opoNTOPOLys, Gabb. Resembles the subgenus Pteronotus in 
having three varices on each whorl, but distinguished by the 
crenulations of the outer lip and by having two transverse plaits 
or folds on the middle of the columella. JZ. compsorhytus, Gabb 
(xliii, 4). Eocene; Wheelock, Texas. 
* * Varices four to ten. 
RHINOCANTHA, H. and A. Adams. Has the short body-whorl 
and long canal of the typical Murices ; differs in having more 
numerous varices. M. cornutus, Linn. (xliii, 5). 
HOMALOCANTHA, Mérch. Whorls rounded and sutures very 
deep; varices foliated, and peculiarly produced into expanded 
digitations ; canal long. JM. scorpio, Linn. (xliii, 6). 
PHYLLONOTUS, Swains. Like Chicoreus, but varices numerous. 
M. radix, Gmel. (xliii, 7). 
b. Operculum purpurotd. 
* Varices three. 
cEROSTOMA, Conrad. Varices wing-like; aperture usually den- 
tate within the outer lip, with a produced tooth near its base. 
Analogous with Pteronotus. It is very difficult to define the 
boundary between this group and Pteronotus, inasmuch as the 
operculum of several of the species is not known; moreover, 
the labral tooth does not always appear even in those species 
having a purpuroid operculum. All the species with more than 
one inter-variceal node appear to be true Pteronoti, and the dis- 
tribution of the group is mainly Indo-Pacific; Cerostoma, on 
the other hand, is North Pacific in distribution, extending from 
Japan northwards to Behring’s Straits, and on the opposite 
American coast south to Central America. WM. Nuttallii, Conr. 
(xlili, 8). 
** Varices numerous. 
VITULARIA, Swainson. Shell oblong ; spire short ; body-whorl 
8 
