Casey — Notes on the Pleurotomidae. 131 



sinus, and a conspicuous system of lines of growth, bi- 

 oblique toward the peripheral carina and composed of exca- 

 vated lines, which are less evident in the very early forms 

 and most conspicuous in the modern species. The type is P. 

 cochlearis Con. of the Vicksburg Oligocene. Pleuroliria 

 comprises two groups, which, although strongly resembling 

 each other in general form and type of sculpture, are in reality 

 almost subgeneric in value as shown below : — 



Group 1. — Embryo multispiral and acute. 



Lines of growth less pronounced, uneven and never deeply incised; species 



small in size and older geologically 2 



Lines of growth deeply incised and conspicuous 3 



2 — Shell rather slender, each of the spire whorls with a moderate sub- 



sutured carina, the surface immediately below it being concave and 

 rather rapidly expanding to a stronger peripheral carina perfectly 

 smooth and uniform, and situated at some distance above the middle, the 

 surface thence cyclindric or very feebly descending to the suture below 

 and having two slightly smaller and somewhat approximate carinae at the 

 middle, the lower margin also carinulate. The two carinae below the 

 periphery become more widely separated on the larger whorls, sub- 

 equally trisecting the space between it and the lower margin, and, on 

 the body whorl, continue thus unaltered to the base of the shell. The 

 concave surface above the periphery has a fine spiral thread above the 

 middle. Embryo moderately stout, conical, closely coiled, rather 

 higher than wide, with five whorls, the four upper smooth, broadly, 

 evenly convex and polished, the lowermost with longitudinal riblets; 

 beak moderately long, the aperture proportioned nearly as in cochlearis. 

 Length of a specimen having 5 body whorls, 9 mm.; width, 2.7 mm. 



Lower Claiborne Eocene of St. Maurice, La simplex n. sp. 



Shell nearly as in the preceding but with the embryo shorter and stouter, 

 fully as wide as high and not evenly conical but becoming substyliform 

 toward the very acute tip, of five whorls, the lowermost covered with 

 riblets. Spire whorls shorter; carinae below the periphery more equal 

 and close- set, the peripheral carina fiuely, obtusely crenulate. Length 

 of a specimen of 2 body whorls, 3.4 mm.; width, 1.2 mm. Lower Clai- 

 borne Eoceue of St. Maurice , crennlosa n. sp. 



3 — Embryo of four whorls, evenly conical, short, fully as wide as high, the 



upper three whorls smooth polished and broadly convex, the lowermost 

 bearing acute but rather widely spaced longitudinal riblets. Shell rather 

 short and stout, with slender beak, the spire whorls very short, each 

 with two strong thick and equal carinae, one just below the suture, the 

 other near basal third; between the latter and the basal margin there is 

 a fine spiral thread first appearing on about the third whorl; lines of 

 growth only moderately distinct and somewhat irregular. Length of a 

 specimen having 3 body whorls, 4.5 mm.; width 1.7 mm. Jacksonian 

 Eocene of Montgomery, La , jacksouella n. sp. 



