GASTEROPODA. 145 
another shell of the same general character, but varies from this in 
the varices and sculpture. 
Figures 166, 166 a, two views of the shell. 
CERITHIUM SORDIDULUM (Gould ). 
Testa elongata, rubiginoso-albida, costellis numerosis et filis volventibus 
alternatim majoribus reticulata: spira turrita, acuminata, anfractibus 
undecim planulatis, ultimo varicoso, granuloso ; sutura profunda : 
apertura ampla, ovato-rotundata ; labro crenulato, extus incrassato, 
rufo-tincto ; rostro attenuato, valde recurvo ; fauce alba. 
Cerithium sordidulum, Goutp; Proceed. Boston Soc. Nat. Hist., 
iii. 119. May 1849. Expedition Shells, 61. 
Suetu slender, elongated, and acutely pointed; white, tinged with 
rusty. Whorls eleven, rather flat, having on each about six, alter- 
nately larger, revolving threads, and numerous (fifteen on the last 
whorl but one), delicate, sharp, equal, regularly disposed ribs, forming, 
where they intersect the larger revolving threads, brilliant granules ; 
on the last whorl, opposite the aperture, is a varix, and below this 
the ribs are wanting; the revolving threads become finely beaded, and 
around the canal simple. The suture is deep, and the whorl above it 
shelves somewhat over it. Canal elongated, and strongly recurved. 
Aperture large, rounded; the lip sharp and very finely crenulated ; 
externally fortified by a strong varix; callus of the columella erect, 
and the whole edge of the aperture delicately tipped with rufous. In- 
terior smooth and white. 
Length seven-tenths of an inch ; breadth one-fourth of an inch. 
Figures 170, 170 a, two views of the shell, enlarged ; 1706, natural 
size. 
Closely allied in size, form, sculpture, and aperture to C. muscarum, 
Say, but distinguished from all others by its delicately tinged peri- 
stome. In its general structure, especially in the development of the 
37 
