PROSOBRANCHIATA. 209 
No. 135. PLEURoTOMA HELIX, 7. HL. Hdwards. Tab. XXV, fig. 7 a, 6. 
P. testa elongato-fusiformi, sub-turritd, fasciis spiralibus, lineis incrementi asperatis, 
cincta ; spird elevatd : anfractibus convewis ; marginibus posticis latis, cavatis, lineas con- 
centricas filiformes inequales gerentibus, ad suturam crenulatis ; fasciis spiralibus angustis, 
numerosis, alternatim majoribus et minoribus: aperturd elongato-ovali, in canali longo ter- 
minantt ; labro valde arcuato ; sinu angusto, profundo, 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. r7cva), 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, 11-12ths of an inch. 
Localities.—Primrose Hill and Potter's Bar. 
No. 136. PLEUROTOMA syMMETRICA. J. #. Hdwards. Tab. XXV, fig. 5 a, 6. 
P. testa elongato-fusiformi, gracili, spiraliter fasciatd, in juventé costulaté; spird 
elevatd : anfractibus convexiusculis, marginibus posticis vie cavatis, ad suturam marginatis, 
erenulatis ; ultimo anfractu in canali longo exeunti ; fasciis spiralibus irregularibus, lineis 
incrementi asperatis : apertura ovali elongata ; labro valde arcuato ; sinu mediocriter lato, 
parum profundo, 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 
