40 SYNOPSIS OF THE CHARACTERS OF THE 



Pleueotomaeia concentrica. Phil. 



Pleurotomariaconcentrica. Phil. Geol. York. 



Sj). Ch. — Conical; whorls quadi'ate, plain above ; surface spirally sulcated ; basal sulci largest. No um- 

 bilicus. 



There are about five turns in the spire ; the quadrate form of the whorls, and spirally sulcated surface, dis- 

 tinguish this from all the species except P. canaliculata, M'Coy, from which it is distinguished by having a 

 distinct angle separating the flat upper part of each whorl from the lower, instead of a concave smooth groove, 

 as in that species. Diameter eleven lines, height of spire ten lines. 



Pleurotomaria conica. Phil. 



Pleurotomaria conica. Phil. Geol. York. 



Sp.Ch. — Acutely conical; height of spire nearly equal to the diameter of the base, umbllicate, band 

 formed of two or three keels, surface with sharp, oblique stria. 



This shell has the spire higher, in proportion to its width, than most of the other species ; there are usually 

 three keels on the band, but sometimes there are only two ; the oblique striae of the surface are beautifully 

 sharp and distinct. Diameter one inch four Hnes, height of the spire one inch three lines. 



Pleueotomakia decussata. M'Coy. (PL V. fig. 13). 



Sp, Ch. — Conical, acute, spire of about five or six whorls; volutions flattened; band broad, flat, defined, 

 placed low down on the basal whorl, and close to the suture on those of the spire ; surface decussated by rough, 

 spiral, and oblique striae ; umbilicus very small. 



This species has the size and form of the P. conica, Phil., but has only one simple, broad, flattened keel, 

 instead of the two or three narrow ones of that species ; besides which the surface of the present shell is marked 

 by strong spiral as well as oblique strise. Length one inch two lines, diameter of basal whorl one inch two 

 lines. 



Pleueotomaeia lenticula. M'Coy. (PI. VII. fig. 5). 



Sp. Ch. — Discoid, very much depressed, smooth; spire of five or six slightly convex whorls, nearly flat, 

 tip mammillary, base flattened ; umbilicus very small, rounded ; a narrow, sharp keel surrounding the last whorl ; 

 surface perfectly smooth. 



This species is remarkable for its very depressed form, the height of the spire being little more than a third 

 of the diameter ; the whorls are all very smooth, and but little convex ; the keel is only visible on the last 

 whorl ; it is very narrow and sharp. Diameter one inch nine lines, height of spire nine lines, thickness of last 

 whorl six lines. 



Pleurotomaeia filosa. M'Coy. (PI. V. fig. 14). 



Sp. Ch. — Whorls very convex both above and below the keel, which is very large, prominent, rounded; 

 surface with close, spiral, thread-like striae both above and below the keel. 



This species is distinguished by its numerous fine, spiral, stria? and large keel ; there are about twenty 

 spiral strice between the keel and the suture above, alternately larger and smaller. Diameter of basal whorl 

 fourteen lines. 



Pleueotomaeia Geiffithii. M'Coy. (PI. VI. fig. 1). 



Sp. C/i.— Acutely conical; whorls flat, base convex; a single, very prominent, square keel, in the middle 

 of tlie body whorl, but continued along the base of the spiral whorls, close to the suture ; umbilicus large, open, 

 conical. 



