192 Prof. F. M'Coy ow some neio Carboniferous 



height of last whorl y^^^^, height of penultimate whorl y^u^ 

 width of mouth /y*^. 



Var. /S. Very elongate conic ; apical angle about 40° ; whorls 

 moderately convex ; base of basal whorl gradually prolonged, 

 not flattened nor separated by an angulation from the sides ; 

 mouth a little longer than wide. Length of last whorl 11 lines, 

 proportional width y^^, height of penultimate whorl y*^%. 



It will be seen that this species has two extreme varieties 

 somewhat resembling those of the P. ynanni ; the variety a so 

 exactly resembles a Trochus, that it requires the most careful ex- 

 amination to detect the extremely obscure, though definite band, 

 to convince the observer that it is a Pleurotomaria ; the var. /S, 

 with the basal whorl elongate and rounded in front or at base, 

 like the corresponding variety of P. yvanni, is so like a Macro- 

 chilus, that it is only by carefully tracing the intermediate forms 

 and detecting the very obscure band, noting the same number of 

 spiral ridges on the whorls, &c. that I have become satisfied of 

 their identity ; both varieties have usually only four whorls pre- 

 served, the posterior end of the animal at that length depositing 

 convex imperforate diaphragms, and becoming naturally decol- 

 lated. 



Both varieties I'are in the impure lower limestone of Lowick, 

 Northumberland; the var. /8 rare in the similar limestone of 

 Kendal. 



Pleurotomaria erosa (M^Coy). 



Desc. Orbicular, depressed, very obtusely conical; apical angle 

 105° ; spire of 4^ rapidly enlarging whorls ; flattened or very 

 slightly convex ; sutures fine, simple impressed lines ; body- 

 whorl flattened or slightly convex in the upper two-thirds, the 

 periphery very obtusely rounded, close to the broad flattened 

 gently convex base ; umbilicus entirely closed, with a large, 

 very thick, semicircular shelly pad ; broad, narrow, obscure, 

 bounded by two fine impressed lines ; surface glossy, eroded 

 with deep, obtuse, excavated markings without regularity in 

 size, shape or direction ; lines of growth arching backwards to 

 the band, scarcely visible. Diameter 5 lines, proportional 

 height ^-^f-^^, height of mouth jj^jj, space between last and pe- 

 nultimate sutures y'^^^^, width of umbilical pad y^jj. 



The band of this species is often almost invisible on the peri- 

 phery of the body-whorl, and the lines of growth can only be 

 traced here and there with a lens. The substance of the shell 

 is very thick, and with the glossy surface, general form, and 

 large umbilical pad recalls Rotella {Pithonellus) very strongly. 



