210 EOCENE MOLLUSCA. 
(8—10) slightly convex ; the posterior margins narrow, very slightly depressed, rather 
thickened at the edges, and presenting round the suture two raised lines, obscurely 
granulated ; in front of these, two or three fine, thread-like lines run along the middle 
part of the margin, granulated by the lines of growth, which are much elevated until 
they cross the shoulder, and give a wrinkled appearance to the margin. The spiral 
bands over the other parts of the whorls are numerous, irregular, and unequal ; smaller 
ones alternating with large ones. The aperture is narrow, and of an oblong-oval 
form; the outer lip arched, and the sinus, which is moderately wide, and not very 
deep, is placed in the front part of the margin, immediately behind the shoulder. 
In the ornamentation the present species resembles P. heliz, but the narrow posterior 
margin, the position of the sinus, and the slight but nearly regular convexity of the 
whorls, giving a symmetrical appearance to the shell, distinguishes it as well from 
that species as from P. erassa. 
Size.—The largest specimen figured would be, if perfect—axis, nearly 4 inches ; 
diameter, 1 inch. 
Localities.—Potter’s Bar, Chalk Farm, Southampton, Shenfield. 
No. 137. PLEUROTOMA TERETRIUM. F. &. Edwards. Tab. XXV, fig. 8 a—s. 
P. testa elongata, fusiformi, spiraliter lineatd : anfractibus convexiusculis, marginibus 
posticis concavis, concentrice lineatis, ad suturam marginatis ; suturis perspicuis ; ultimo 
anfractu valde producto, in canali longo exeunti ; lineis spiralibus irregularibus, alternatim 
Suniculosis et tenuibus, lineis incrementi per-asperatis ; apertura elongato-ovali ; labro valde 
arcuato ; sinu lato, profundo, in margine collocato. 
Var. NANovis. Testd breviori, latiori ; marginibus posticis anfractuum pauaillum 
cavatis. 
Var. CREBRILINEA. Testd minori, graciliori : anfractibus obsolete tuberculatis, lineis 
sprralibus numerosis, equalibus, fortiter decussatis. 
Var, TuBERCULATA. Testd graciliori: anfractibus sub-angulatis, tuberculatis, ad 
suturam crenulatis : lineis spiralibus confertis, sub-equalibus. 
Var. LATIMARGINATA. Tesla minori: spird tuberculatd: marginibus anfractuum 
latissimis, contra spiram expressis. 
Shell elongate, fusiform, ornamented with numerous spiral, raised lines; spire 
elevated, formed of 7—9 volutions: whorls somewhat convex, separated by a perspi- 
cuous suture, and much produced in front, the last whorl terminating in a long, nearly 
straight canal; the posterior margins concave, slightly thickened, and occasionally feebly 
crenulated at the edge. The spiral lines over the middle and front parts of the whorls 
are irregular, thickish, cord-like bands, alternating with slender, thread-like lines, and 
