CARBONIFEROUS LIMESTONE FOSSILS. 261 



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 rare in the impure lower limestone of Lowick, 

 Northumberland; the var. /3. 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 ; band 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 -y-qq, height of mouth -^-§0) space between last and pe- 

 nultimate sutures y^q, width of umbilical pad y^^^^. 



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 [PithoneUns) very strongly. 

 The peculiar " worm-eaten '' appearance of the irregular pitting 

 of the surface is equally marked in the two specimens before me. 



Rare in the carboniferous limestone of Lowick. 



{Col. University of Cambridge.) 



Macrochilus limnaiformis (M^Coy). 



Desc. Elongate fusiform, very acutely rhomboidal, greatest 

 width at about the middle of the total length, from whence 

 the anterior or basal part is conoidally attenuated or rapidly 

 sloped to the greatly narrowed front of columella, and very 

 rapidly sloped to the suture, which is simple and slightly im- 

 bricating ; spire very abruptly attenuated, long, very slender ; 

 sides very concave in the profile of about six or seven whorls 

 (usually five preserved) ; apical angle 54° ; surface polished 

 very smooth, with occasionally fine traces of obsolete direct 

 lines of growth ; mouth narrow, elongate, contracted before 

 and behind ; anterior part of columella very slightly thickened. 

 Length about 1 inch 7 lines, proportional length of mouth of 



