PAPERS ON GEOLOGY AND GEOGRAPHY 205 



pears to radiate from the beak, and the other set crosses the first with a curva- 

 ture that trends forward and downward from the vicinity of the beak, crossing 

 the first set at an angle somewhat less than 90 degrees. 



The left valve was not seen. 



The dimensions of the type are: Length 9 mm., height 5 mm., thickness of 

 right valve 3 mm. 



Remarks: — This shell is most nearly like Cypricardinia indenta Conrad, from 

 the Hamilton of New York and the East, from which it differs in the smaller 

 size, the greater height in proportion to the length, in the less extended postero- 

 ventral border, the shorter hinge line, and in the peculiar ornamentation of the 

 surface of the shell. 



Horizon and Locality: — It occurs in the Cedar Valley stage of the Devonian 

 near Andalusia, in Rock Island County, where it is associated with the species 

 of Cranaena above described. 



POTERIOCERAS GIGANTEA N. SP. 

 Plate III. 



Description: — Shell large, subelliptical to ovate in cross-section, somewhat 

 curved throughout, the curvature slight on the concave side, but rather strong 

 on the convex; the greatest curvature is a short distance posterior to the base 

 of the body chamber. The length of the preserved part of the shell is 18 

 inches, the diameter of the posterior end of the specimen is 2 inches, several 

 of the lower chambers having been lost. The length of the entire shell must 

 have exceeded 20 inches. The shell is somewhat flattened in the direction of 

 the curvature; the largest part of the shell is at the second septum posterior 

 to the body chamber where the greatest diameter is 7 inches and the smallest 

 diameter is nearly 4^ inches. Posterior to this the greatest width decreases 

 rather uniformly at the rate of lYz inches in a distance of 6 inches. The 

 septa are moderately concave, the average width of the chambers in the larger 

 part of the shell is 3/5 of an inch, and the average Avidth of the posterior 3 

 inches of the shell is 1/3 of an inch. The body chamber is 4^ inches long, 

 and has a greatest width of 6^ inches at the posterior end. Anteriorly the 

 width decreases slightly, being a little more than 5 inches at the place of 

 greatest constriction immediately below the aperture. The aperture is mostly 

 concealed, but it is produced somewhat in the direction of the greatest diameter 

 of the shell. The size and position of the siphuncle are not clearly shown, and 

 the surface markings of the shell are unknown. 



Remarks: — This form differs from every other species of the genus known 

 to the writer in its very large size. In shape it somewhat resembles Poterioceras 

 hyatti Whitfield, but the latter is much smaller, and is considerably wider in 

 proportion to its length. The relation of the greatest width and the greatest 

 curvature is also different from that of the species above described. 



Formation and Locality: — Occurs in the upper part of the Wapsipinicon 

 limestone, a short distance above the strongly brecciated bed, in the old 

 quarry at Sears, near Rock Island, Illinois. 



RHYTICERAS ORNATA N. SP. 

 Plate IV. 

 Description: — Shell rather large, regularly expanding, loosely coiled in a 

 little more than two volutions; the greatest diameter is 10^ inches; in the 

 internal cast the distance between the volutions in the middle portion is about 

 \y^ inches, but the whorls approach to about ^ inch apart towards the body 

 chamber. The transverse section is subcircular or slightly elliptical, the lateral 

 diameter being a little greater than the dorsi-ventral. The greatest diameter of 

 the whorl (cast) is slightly more than 2^ inches; the original shell was 

 doubtless 3 inches in diameter. The greater part of the body chamber is lack- 

 ing in our specimen, and the aperture can not be seen. The septa are smooth, 

 their concavity about equalling the depth of the chambers, which is about ^ 

 of an inch near the aperture of the shell, and about % inch near the middle, 



