NATURAL SCIENCES OP PHILADELPHIA. 463 



of the last turn, very deep and permitting the inner side of all the volutions to 

 be seen to the summit of the spire. Surface marked by fine, rather obscure 

 lines of growth. 



Heighth 0-88 inch; breadth 1-08 inch; breadth of umbilicus, measuring from 

 its marginal angle on the middle of the underside of last whorl, 0-68 inch; 

 apical angle convex, divergence about 100. 



Locality and position. St. Clair County, Illinois. Lower Coal Measures. 



Genus NATICOPSIS, McCoy. 



Naticopsis nodosus. Shell obliquely subrhomboidal, rather thick; spire 

 depressed; volutions four and a-half, convex, increasing rapidly in size, last 

 one large, gibbous, oblique, and composing three-fourths of the entire length, 

 round on the outer side, and having shallow revolving depressions near the 

 suture above; suture moderately distinct; aperture subovate; lip sharp; 

 columella distinctly flattened, somewhat callous, not perforated. Surface 

 ornamented by numerous, nearly round, distinct nodes, which are arranged in 

 oblique rows, parallel to the lines of growth near the aperture of the last 

 turn, but become more crowded, and show a tendency to assume a quincunx 

 arrangement on other parts of the shell; lines of growth fine, rather regular 

 and scarcely deflected from their course by the presence of the nodes. 



Length, measuring from the most extended part of the aperture below, 

 obliquely to the apex of the spire, 1 inch; breadth 0-52 inch; apical angle 

 convex, divergence about 96. 



Locality and position. St. Clair County, Illinois. Lower Coal Measures. 



Naticopsis Hollidayi. Shell obliquely oblong-oval, thick and solid ; spire 

 depressed subcorneal, pointed at the immediate apex; volutions four to four 

 and a-half, convex, excepting just below the suture, where there is a shallow 

 revolving depression, rapidly enlarging, the last one forming more than 

 two-thirds the entire length;, suture linear; aperture ovate around the margin, 

 but contracted by the broad columella so as to be nearly semicircular within; 

 columella distinctly flattened, broad, and marked along its sharp, nearly 

 straight inner margin, by a well defined opercular impression. Surface 

 ornamented by very fine regular lines of growth, and numerous small nodes, 

 arranged in oblique rows ; the larger nodes on the last half and upper part of 

 the body whorl being more or less elongated in the direction of the lines of 

 growth. 



Length 1-15 inches; breadth 1-20 inches; apical angle nearly regular, 

 divergence 107. Named in honor of Mr. George H. Holliday, of Carinville, 

 Macoupen County, Illinois, to whom we are indebted for the specimens 

 described. 



Locality and position. Hodges Creek, Macoupen County, Illinois. Coal 

 Measures. 



Genus PLATYOSTOMA, Conrad. 



Platyostoma nana. Shell quite small, subglobose, wider than high; spire 

 much depressed; volutions three, increasing very rapidly in size, last 

 one large and ventricose; suture rather deeply defined; aperture large, 

 broad obovate, straight on the inner side, equalling nearly seven-eighths of 

 the entire length of the shell; surface marked by fine lines of growth, which 

 become stronger, and very regular near the suture on the upper side of the 

 whorls. 



Length 0-19 inch; breadth 0-21 inch; length of aperture 0-15 inch, breadth 

 of do. 0-11 inch; apical angle about 123. 



Differs from P. Peoriensis, McChesney, in being much smaller, and in having 

 one whorl more, while its aperture is widest above instead of below. 



Locality and position. Springfield, Illinois. Upper Coal measures. 



Platyostoma? tumida. Shell rather large, thin, subpyriform, a little longer 

 I860.] 



