Limestone Fossils. 191 



Murchisonia dispar (M'Coy). 



Desc. Elongate, very acutely conic ; apical angle 30° ; spire of 

 about eight very gradually increasing tumid whorls ha^'ing a 

 very thick obtuse prominent band, forming a rounded keel 

 much nearer the lower than the upper suture ; upper and lower 

 surfaces slightly tumid, convex, the lower portion most steeply 

 sloped ; the band is either simple, or rarely with three spiral 

 striae ; two strong spiral lines below the keel, and six slightly 

 smaller ones above it on each whorl ; base of body- whorl 

 rounded, convex, with an obtuse angulation at such a distance 

 below the keel, that it is just concealed by the sutui-e on the 

 spiral whorls ; lines of growth five, unequal, obscure, slightly 

 arched, oblique to the band. Length 7 lines, proportional 

 width -^^^f height of last whorl -^^^, height of penultimate 

 whorl -?-^~ 



This species is easily distinguished from its allies, the M. sub- 

 sulcata and M. Archiacana, De Koninck, and M. Larconi, M'Coy, 

 by the disparity in width of the parts of the whorls above and 

 below the band, and the disparity in number of the keels or 

 spiral striae which ornament those parts. 



Not very uncommon in the impure carboniferous limestone of 

 Lowick, Northumberland. 



{Col. University of Cambridge.) 



Pleurotomaria decipiens (INPCoy). 



Desc. Var. a. Spire acute, regularly conic ; apical angle about 

 40" ; composed of about seven or eight gradually increasing 

 flat whorls ; suture a simple impressed line ; base of body- 

 whorl flattened, forming a strong angle with the spire; no 

 umbilicus ; pillar-lip slightly thickened, arched ; mouth ob- 

 long angulated, a little wider than long ; surface marked with 

 narrow thread-like spiral ridges, separated by tiat or slightly 

 concave spaces about three times their width ; about eight or 

 nine spiral ridges on each whorl, and seven or eight more 

 rather stronger on the base, the intervening spaces very irre- 

 gularly cancellated by obscure, unequal, obtuse, longitudinal 

 wrinkles, very slightly oblique to the band, forming an obscure 

 irregular, quadrate pitting, occasionally visible on the cast, 

 these transverse plicae closer and more oblique on the base ; 

 band about the width of the ordinary spaces between the spiral 

 lines, flat, very inconspicuous, and bounded by ver\' delicate, 

 impressed lines, destitute of the obtuse cancellating plicae of 

 the rest of the surface, situated two inter-spiral spaces above 

 the lower suture of each whorl. \V idth 10 lines, proportional 



