PROSOBRANCHIATA. 269 
and front part of the whorl, but become obsolete over the middle and upper parts, 
so as not to detract from the otherwise smooth and shining surface. The aperture is 
of a narrowish, oval form ; the outer lip arched, projecting slightly towards the front, 
thin, sharp-edged, and smooth within ; and the sinus wide, nearly semicircular, and 
extending across the whole width of the margin. 
The characters of this Pleurotoma are sufficiently well marked to merit distinction. 
Although presenting a close resemblance to Plewrotoma tereticosta in the general 
appearance, yet the smooth and shining surface of the shell, the more obtuse spire, the 
greater width of the whorls, the thicker and more distant ribs, the more conical 
form of the body-whorl, and the different condition of the sinus, separate the two 
species. 
Size.—Axis, 5-]2ths of an inch; diameter, 2-12ths of an inch. 
Locality.—Potter’s Bar. . 
No. 192. Prevroroma Fisnert. F. 2. Edwards. Tab. XXXII, fig. 14, a, 4. 
P. testé elongata, turriculatd, longitudinaliter costatd, concentrice lineatd: spird 
productd, acuminata: anfractibus brevibus, convewis, ad humeros angulatis; marginibus 
posticis latis, depressis, paululo cavatis, ad suturam tuberculatis ; cetertim levibus ; ultimo 
anfractu sub-conico ; costellis latiusculis, rotundatis ; lineis concentricis antice distantibus ; 
supra partes medianas anfractium numerosioribus, irregularibus ; supra margines posticas 
obsoletis: apertura ovali, in canali brevi, lato exeunti; sinu lato, sub-trigono, anticad im 
margine collocato. 
Shell long, narrow, turreted, longitudinally ribbed, and spirally lined; the spire 
pointed and much produced, forming nearly two thirds of the whole length of the 
shell. The whorls, seven or eight without the pullus, are short, angular at the 
shoulders, and nearly conical in front; the posterior margins wide, depressed, a little 
concave, and smooth, except on the sutural edge, where they present a single row 
of rather large and distant rhomboidal knobs, divided by a transverse furrow across 
the middle. The longitudinal ribs are short, broad, nearly vertical, rounded on 
the upper surface, and separated by concave spaces as wide as the ribs, which, 
in the last whorl, become reduced to oblong tubercles. The transverse lines are 
sharp and elevated, distant, and separated by smooth, flat spaces over the front of the 
whorls, but they become more numerous and irregular as they ascend the whorl from 
the middle towards the shoulder, and are altogether lost on the posterior margins. 
The mouth is of an oval form, and terminates in front in a wide and short, but 
distinct canal; the outer lip is thin, sharp-edged, and slightly arched, and the sinus, 
which is placed in front of the margin, is wide and somewhat triangular in shape. 
This Pleurotoma approaches most nearly to P. gomphoidea, but the more turreted 
