Casey — Notes on the Pleurotomidae. 155 



covered with hue acute longitudinal riblets. The periphery 

 is more or less obtusely swollen, the ribs small and numerous 

 and reduced in size and reversed in curvature on the broad 

 fasciolar surface, generally attaining the suture or small sub- 

 sutural collar above. The canal is rather tapering in form, 

 straight, moderate in length, and, together with the aperture, 

 about half as long as the shell. Of the two following species 

 the first is to be regarded as the type : — 



Shell very small, with two or three body whorls, moderately stout, the em- 

 bryo of five whorls which gradually and evenly increase in size, the 

 apical whorl or nucleus very minute, acutely rounded and relatively 

 higher in form, the second to fifth broadly convex and closely covered 

 with an elaborate system of fine riblets, becoming more widely spaced 

 on the fifth and gradually merging without break into the ribs of the 

 subsequent whorls; these ribs are some twelve in number, elevated, 

 rounded, extending throughout the couvexity of the body whorl below 

 and to the very fine subsutural collar above, becoming reduced and 

 arcuately reversed in curvature across the fasciolar surface; spiral 

 lines moderately coarse, even and flat, rather widely spaced and without 

 intermediate lines, becoming close- set near the base and slightly 

 smaller and more close-set on the fasciolar surface. Length of a speci- 

 men of 2 body whorls, 4.8 mm.; width , 1.5 mm. Lower Claiborne 

 Eocene of St. Maurice, La nacleola n. sp. 



Shell slightly larger and rather more slender, with more elevated and less 

 obtusely rounded periphery, the aperture and canal combined notice- 

 ably shorter than the remainder; embryo relatively larger, higher than 

 wide, of about five whorls, the four uppermost smooth, forming a large 

 even cone, the two lower whorls of which are relatively more inflated 

 toward base, the fourth acquiring coarse feeble riblets which grow 

 stronger on the fifth, where they are broadly arcuate and widely spaced ; 

 the fifth whorl is large, and more evenly convex and gradually acquires 

 spiral sculpture but no defined peripheral swelling; subsequent whorls 

 with about eighteen small but distinct ribs, gradually becoming obso- 

 lete at the lower margin, attenuated and arcuate in reverse on the fasci- 

 olar surface but not quite attaining the rather distinct cariniform sub- 

 sutural collar; on the second body whorl the ribs form acute nodules 

 on the peripheral ridge but do not extend materially below the latter, 

 and, while still distinct on the fasciolar surface, come still further from 

 attaining the subsutural collar; spiral lyrae on and below the peri- 

 phery moderately coarse, even, well spaced and without intermediate 

 threads, becoming close-set on the beak; on the fasciolar surface they 

 are finer and close-set. Length of a specimen of 2 body whorls, 6.4 

 mm. ; width, 2.0 mm. Lower Claiborne Eocene (from a well seven miles 

 south of Jewett, Texas) — Mr. T. H. Aldrich bellala n. sp. 



This genus will also include P. georgei Harr., from the 

 Lignitic Eocene of Wood's Bluff, Ala., and an undescribed 



