PROSOBRANCHIATA. 209 



No. 135. Pleurotoma helix, F. E. Edwards. Tab. XXV, fig. 7 a, b. 



P. testa elongato-fusiformi, sub-turritd, fasciis spiralibus, lineis incrementi asperatis, 

 cinctd ; spird elevatd : anfractibus convexis ; marginibus posticis latis, cavatis, tineas con- 

 centricas filiformes incequales gerentibus, ad suturam crenulatis ; fasciis spiralibus angustis, 

 numerosis, altematim majoribus et minoribus : aperturd elongato-ovali, in canali longo ter- 

 minanti ; labro valde arcuato ; sinu angusto, prof undo, in margine collocato. 



Var. ricna. Testa anfractibus sub-angulatis ; fasciis spiralibus numerosioribus, tribus 

 minoribus inter majores apparentibus. 



Shell lengthened, fusiform, and covered with concentric bands, roughened by the 

 strongly marked lines of growth ; spire elevated : whorls convex, rounded at the 

 shoulder, produced in front ; the posterior margins wide, channeled, and bordered 

 round the suture by two or three bands strongly crenulated ; the middle of the margin 

 presents three coarse, rounded, raised lines, and on each side of these three or 

 more fine thread-like lines. The line of the suture is very decurrent, and runs at some 

 distance below the wide part of the whorl, giving a screw-like appearance to the spire. 

 The spiral bands are numerous, rounded at the edges, and unequal, the alternate ones 

 being smaller than the others. The aperture is of a narrow, ovate form, and terminates 

 in a longish straight canal ; the outer lip is much arched, and the sinus, which is deep 

 and moderately wide, is placed in the middle of the margin. 



Specimens occur at Potter's Bar (var. ricna), in which the shoulders of the whorls 

 are angulated, and a fine thread-like line runs on each of the smaller spiral bands. 



The specimens figured were obtained from the railway cutting at Primrose Hill, 

 and form part of Mr. Wetherell's collection. 



Size. — The exact dimensions cannot be given, but those of the largest specimen 

 figured must have been — axis, nearly 3 inches; diameter, ll-12ths of an inch. 

 Localities. — Primrose Hill and Potter's Bar. 



No. 136. Pleurotoma symmetrica. F. E. Edwards. Tab. XXV, fig. 5 a, b. 



P. testa elongato-fusiformi, gracili, spiraliter fasciatd, in juventd costulatd ; spird 

 elevatd: anfractibus convexiuscutis, marginibus posticis via; cavatis, ad suturam marginatis, 

 crenulatis ; ultimo anfractu in canali longo exeunti ; fasciis spiralibus irregularibus, lineis 

 incrementi asperatis : aperturd ovali elongatd ; labro valde arcuato ; sinu mediocriter lato, 

 par um prof undo, in margine collocato. 



Shell lengthened, slender, fusiform, ornamented with numerous spiral bands, and, 

 in the early stages of its growth, obscurely ribbed : spire elevated, pointed : whorls 



