NATURAL SCIENCES OF PHILADELPHIA. 19 



Height when resting on the aperture *32 ; summit in this position two- 

 thirds the distance from the aperture to the apes ; width of aperture "33. 



Platyceras vomerujm, n. sp. Shell of medium size, describing about half 

 a direct whorl, very rapidly enlarging ; peripheral (or dorsal) region elevated 

 and surmounted by a strong, broad, rounded carina, which becomes more ob- 

 tuse toward the aperture, a shallow groove running along each side of the 

 carina ; transverse section showing an angle of about 70 toward the beak, 

 which enlarges to about 110 near the aperture ; surface of cast destitute of 

 markings. 



Distance from front of aperture in a straight line, to most projecting por- 

 tion of beak *85 (100) ; height of shell when resting on the aperture *47 (55) ; 

 summit when in this position three-fifths the distance from aperture to apes ; 

 length of aperture -67 (79) ; width of aperture -58 (68). 



This sharp-backed species approaches P. carinatum, Hall, (Fourteenth Rep. 

 N. Y. Reg., p. 5,) but differs in being equilaterally developed. It belongs to the 

 Orthomjchia group, which Prof. Hall has welded to the Neritoid forms under 

 one generic designation. 



Believed to range from the base of the yellow sandstones into the base of the 

 Burlington limestone. 



PLEUROTOMARIA, Defrance. 



Pleurotomaria ? rota, n. sp. Shell small ; spire depressed, conves, con- 

 sisting of four or five flattened whorls ; suture sharply channelled as if by the 

 rabbet of a joiner. Base of shell unknown, but a solid asis in the cast of the 

 spire would indicate a deeply perforate umbilicus. No surface markings. 

 "While the imperfect specimens plainly indicate an undescribed species, it 

 is as yet impossible to determine the generic position of the shell. 

 Ranges from bed No. 5 into the base of the Burlington limestone. 



Pleurotomaria tectoria, n. sp. Shell small; spire trochoid, consisting of 

 about four whorls, flattened between the periphery and the suture ; peri- 

 phery marked by a raised, somewhat bicarinate band ; a raised carina running 

 along the upper margin of each whorl close to the suture ; base rounded reg- 

 ularly from the periphery to a small, sunken, perforate umbilicus ; aperture 

 suboircular, somewhat modified by the body whorl, angulated posteriorly, 

 rounded in front, the peristome descending into the umbilicus. 



MURCHISONIA, d'Archiac. 



Mcrchisoxia qitadricincta, n. sp. Shell of medium size, turrited ; whorls 

 conves, regularly enlarging to the last, with an obsoletely bicarinate band 

 running along the middle, below which are four small, rigid, thread-like, ap- 

 proximated carinse, leaving the base of the body whorl smooth or faintly 

 lined, and regularly curved into the umbilical cavity ; the surface above the 

 band marked only by very delicate lines of growth, which arch backwards to 

 the peripheral band, below which they arch far forwards, entering the umbili- 

 cal cavity half their length in advance of their place of origin at the suture. 

 Suture deeply impressed. 



The only specimen showing the external markings has a defective spire, 

 but it could not be completed with less than 8 or 9 whorls, giving a length of 

 1-S (100) ; an apical angle of 19, a sutural angle of 66, while the body whorl 

 is -25 (14) high. 



Some internal casts perhaps of the same species have double the above 

 dimensions, and exhibit a shallow longitudinal groove on the penultimate 

 whorl near the suture, which, in the ultimate whorl, becomes a broadly con- 

 cave flattening of the upper region, and a somewhat sharp angulation at the 

 suture. In these, the outer lip is rounded, the inner somewhat excavated, 

 and the aperture is angulated and slightly effuse in front. Still other casts 

 exhibit a more elevated spire, with the smooth, rounded whorls barely in con- 

 1863.] 



