PROSOBRANCHIATA. 227 



state are tuberculated, or roundedly costellated ; the posterior margins are moderately 

 wide, very little depressed, nearly straight, and almost smooth, or ornamented with 

 concentric lines, so faint and slender as to be almost imperceptible without the aid of 

 a magnifying glass; the last whorl is produced in front, and, diminishing very 

 gradually, terminates in a long, nearly straight canal. The aperture is lanceolate ; the 

 outer lip thin, sharp edged, and much arched ; and the sinus, which is very wide, and 

 sub-trigonal in shape, is placed a little in front of the middle part of the margin. 



The long, narrow, lanceolate form, and nearly conical spire of this Pleurotoma 

 distinguish it from all its congeners. 



Size. — Axis, 1 inch and 4-12ths ; diameter, 4-12ths of an inch. 



Localities. — Barton and Alum Bay (No. 29, Prestwich), where it is not very 

 common. 



No, 152. Pleurotoma laevigata, Sowerby. Tab. XXVI, fig. 9 a, b. 



Pleurotoma laevigata, Sow. 1823. Min. Con., vol. iv, p. 120, t. 387, fig. 3. 



— . — Morris. 1843. Cat. Brit. Foss., p. 157. 



— If Orb. 1850. Prod, de Paleont., vol. ii, p. 359, No. 412. 

 Nee Pleurotoma l^vigatum, Phil. 1836. Enum. Moll. Sic., vol. i, p. 199, t. 11, fig. 17. 



nee — l^vigata, De Kon. 1837. Coq. foss. de Basele, &c., p. 27, No. 27, t. 1, fig. 5. 



nee — — Mellev. 1843. Mem. sur les sables infer., &c., de Paris, p. 63, 



t. 8, figs. 9— 11. 



P. testa elonyato-fmiformi, anyustd, turritd, transversim tenuissime lineatd; spird 

 elevatd, acuminata: anfractibus convexis, antice subito coarctatis, prioribus oblique costel- 

 latis ; marginibus posticis anyustis, depressis, sub-canaliculatis, Icevibus ; ultimo anfractu 

 in canali lonyo, anyusto, terminanti : aperturd oblonyd, ovatd ; labro valde arcuato, tenui; 

 sinu lato,/ere semicirculari, in maryine collocato. 



Shell long, narrow, fusiform, turreted, costellated, and spirally lined : the spire 

 elevated, pointed, terminating in a pullus of two round, smooth volutions ; whorls 

 convex, rounded on the shoulders, contracted rather suddenly in front ; the posterior 

 margins narrow, depressed, slightly hollowed out, having the sutural edges thin and 

 quite simple, and the surface smooth, almost polished, presenting only very feeble lines 

 of growth of the sinus. The ribs are distant, rounded, oblique, and extend almost to 

 the front part of the whorl in the young shell, but become shorter and less prominent 

 as the shell enlarges, and altogether disappear on the body-whorl of the fully formed 

 shell ; the spiral lines are very slender, sharp, but little elevated, irregular, unequal, 

 and decussated by the lines of growth. The aperture is of an oblong, ovate form, and 

 terminates in front in a long, narrow, and slightly curved canal ; the outer lip is much 



