206 ILLINOIS STATE ACADEMY OF SCIENCE 



the depth gradually decreasing from the aperture toward the apex. The 

 position of the siphuncle is not clearly shown in our specimen, but appears to 

 be small, and situated near the ventral side, not enlarged in the chambers 

 between the septa. 



The surface is ornamented by a row of prominent nodes or spinous projec- 

 tions about one inch apart along each side, which also appear to mark the 

 position of transverse ridges. Traces of a third row of spines or of a longi- 

 tudinal ridge appear along the ventral margin of the shell. On the dorsal 

 surface of the outer whorl there are preserved in some places rather prominent 

 longitudinal lines or ridges 54 to ^ inches apart; such longitudinal markings 

 probably covered the entire surface of the shell. Numerous fine lamellose lines 

 of growth, some of which appear to be stronger than others, are also conspic- 

 uous on the portions of the shell that are preserved. 



Remarks: — In the surface ornamentation this form is readily distinguished 

 from any other known species of Rhyticeras. It differs from Rhyticeras cyclops 

 Hall in the more gradual enlargement of the whorls, the stronger transverse 

 ridges, more prominent nodes along the lateral and ventral margins, and in the 

 finer longitudinal surface markings. From Rhyticeras spinosum Hall it is 

 distinguished by the stronger longitudinal ornamentation, and less rapid ex- 

 pansion of the anterior part of the shell. 



Formation and Locality: — This species occurs in the upper part of the 

 Wapsipinicon limestone where it is associated with Gypidula comis, Poteri- 

 oceras gigantea, and Rhyticeras barrisi, near the village of Sears, in Rock 

 Island County, Illinois. 



EXPLANATION OF PLATES 



PLATE I. 



Figures 1 and 2. Diplophyllum? major n. sp. Transverse section of two 

 corallites magnified a little more than two times; and view of a fragment of 

 corallum, natural size. 



Figures 3 and 4. Zaphrentis putilla n. sp. Longitudinal view showing 

 septal ridges; and transverse section of a corallite. Both one and one-half 

 times natural size. 



PLATE n. 



Figures 1 and 2. Rhipidomella minima n. sp. Ventral and dorsal views 

 of the type specimen. A little more than twice natural size. 



Figures 3 and 4. Cranaena elliptica n. sp. Dorsal and ventral views of 

 the type; magnified about two times the natural size. 



Figures 5, 6 and 7. Pugnoides subovata n. sp. Ventral, dorsal and front 

 views of a typical specimen. Twice natural size. 



Figure 8. Cypricardinia ornata n. sp. View of the right valve of a nearly 

 entire specimen; enlarged a little more than two times. 



Figures 9 and 10. Cranaena subovata n. sp. Ventral and dorsal views of the 

 type specimen. Enlarged two times. 



Figure 11. Cranaena maxima n. sp. Dorsal view of a typical specimen. 

 About twice natural size. 



PLATE III. 



Figure 1. Poterioceras gigantea n. sp. Longitudinal view of the type 

 specimen. A little less than one-half natural size. 



PLATE IV, 



Figure 1. Rhyticeras omata n, sp. View of one side of an exfoliated 

 specitnen. About one-half natural size. 



