468 PROCEEDINGS OF THE ACADEMY OF 



t ipering into the canal below ; outer lip thin, sharp, and scarcely sigmoid 

 in outline; inner lip none; columella straight, and provided with a single 

 distinct rather sharply elevated, oblique plait or fold, a little below the middle 

 of the aperture; surface smooth, or only showing under a good lens faint traces 

 of very fine lines of growth, 



Length 0-73 inch ; breadth 0-30 inch ; apical angle slightly concave, divergence 

 0-40. Length of aperture and canal, 0-34 inch; breadth of former 0-11 

 inch. 



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



CEPHALOPODA. 



Genus ORTHOCERAS, Breynius. 



Orthoceras expansum. Shell having the form of a moderately compressed, 

 rapidly tapering cone; section subcircular, near the smaller end, but more 

 oval towards the larger. Septa concave, and separated near the smaller end 

 by spaces between one-fourth and one-fifth their own greater diameter; the 

 intervals increasing somewhat, but not near in proportion to the expansion of 

 the shell above; siphuncle subcentral, small where it passes through the septa, 

 but swelling out into a globular cavity between. Surface apparently smooth. 



Length of an entirely septate specimen imperfect at both extremities, 4-29 

 inches; greater diameter at the smaller end 0-80 inch, smaller do. of same 

 about 0-71 inch; greater diameter at larger end apparently not less than 3-20 

 inches. 



This species is allied in form and general appearance to O. dilatatum, 

 DeKoninck, (An. Fos. p. 515, pi. 45, fig. 8, a, b, c), but differs in presenting an 

 oval instead of a circular section ; its siphuncle is also much more nearly 

 central than is represented in DeKoninck's figure 8, a and b, pi. 45, and differs 

 in its peculiarity of swelling out into globular cavities between the septa. Our 

 species seems likewise to differ in its surface markings, being nearly or quite 

 smooth : this, however, may be due, at least to some extent, to the exfoliation 

 of the outer layers of the shell. 



Locality and position. McDonough County, Illinois ; the specimen being found 

 loose, its exact geological position is unknown, though it is doubtless a 

 carboniferous species. 



Genus CYRTOCERAS, Goldfuss. 



Cyrtoceras curtum. Shell rather under medium size, slightly arched and 

 rapidly expanding; section oval, the transverse diameter being greater than 

 from the dorsal to the ventral side; lateral margins a little flattened; ventral 

 and dorsal sides very broadly rounded. Surface ornamented by numerous 

 small, regularly arranged annular striae, or impressed lines, which arch a little 

 forward in crossing the dorsum, where they are separated by spaces several 

 times their own breadth, excepting near the smaller extremity of the shell. 

 On the sides and ventrum, they become much more crowded, and more deeply 

 impressed. Septa rather deeply concave; siphuncle small, and placed about 

 half-way between the middle and the dorsal side. 



Length of a specimen imperfect at the smaller end, 1-25 inches; greater 

 diameter at the aperture about 1-24 inch, smaller do. 0-92 inch; greater 

 diameter at the smaller extremity 0-54 inch, smaller do. 0-45 inch. 



Locality and position. Graysville, Illinois. Coal Measures. 



Cyrtoceras? dilatatum. Shell broadly conical, very rapidly expanding, 

 thick, especially on one side, a little curved and apparently somewhat 

 compressed ; surface ornamented by numerous distinct, regularly arranged, 

 .uibinibricating annular marks of growth: septa separated, at about about two 

 inches from the smaller end, by spaces near one-twelfth of the greater diameter 

 of the shell at the same place; (siphuncle and aperture unknown). Length 



[Oct. 



