PROSOBRANCHIATA. 253 
wide, short, indistinct canal. The spiral lines are slender, thread-like and irregular, 
others, finer still, occasionally intervening ; all are much roughened, almost decus- 
sated, by the prominent lines of growth; from the upper three lines, left uncovered 
by the succeeding whorl, the specific name is taken. The aperture is of a narrow, 
oval form; the outer lip roundedly arched, thin, sharp-edged, and smooth within ; 
and the sinus, which extends over the whole breadth of the margin, is wide, rather 
deep, and somewhat triangular in form. 
The only two specimens I have seen of this rare Pleurotoma do not appear to 
have attained their full growth; the characters, however, are sufficiently distinct 
to justify the present notice. 
Stze.—Axis, 4-12ths of an inch, nearly; diameter, 1-8th of an inch. 
Locality.—Potter’s Bar. 
No. 175. Pxreuroroma pupa. F. £. Edwards. Tab. XXVIII, fig. 9, a—e. 
P. testé elongato-fusiformi, longitudinaliter plicatd, concentrice lineatd: spird obtust- 
usculd, sub-conicd: anfractibus conveeiusculis ; postice plicatis, unico sulco angusto exaratis, 
ad suturam aliquando lined elevatd filiform cinctis, aliquando granulatis ; costellis crebris 
angustis, arcuatis, in ultimo anfractu obsoletis; lineis concentricis acutis, plus minusve 
numerosis, costellas decussantibus: aperturd angustd, ovali, in canali brevi, obliquo 
exeunti; labro leviter arcuato, intis plicato; sinu sub-trigono, profundo, in margine 
collocato. 
Var, a, testd graciliori ; spird acutiori. 
Shell oblong, fusiform, with an elevated, somewhat obtuse, and nearly conical 
spire, forming one half of the entire shell; whorls six or seven, slightly convex, 
longitudinally plicated, concentrically lined, and separated by a conspicuous suture ; 
the posterior margins are thickened round the sutural edge, and present a narrow, 
concentric furrow, corresponding with the smaller extremity of the sinus, and finely 
plicated ; the narrow space between this furrow and the suture is girt by a thickish, 
elevated, thread-like line, generally simple, but sometimes—more especially in the 
early whorls—decussated by the successive margins of the sinus, so as to present 
a row of rather coarse granulations. ‘he longitudinal plications are numerous, and 
curved ; they are slightly prominent on the shoulder, but become attenuated as 
they pass over the middle of the whorl, and are frequently altogether lost on the last 
whorl of the mature shell. The concentric lines are prominent, sharp, more or less 
distant in different specimens, and feebly denticulated, where they cross the lon- 
gitudinal plications. The aperture is of a narrowish, oval form, and terminates 
in front in a short, but distinct and moderately wide, canal, to which the twisted 
columella gives an oblique direction ; the outer lip is slightly arched, thin, and sharp 
