358 TWENTIETH REPORT ON THE STATE CABINET. 



CYRTOCERAS RiaiDUM. 

 PLATE 16 (7), FIGS. 3-5. 



Shell small, consisting of about one volution, gradually expanding to a 

 diameter of three -fourths of an inch with a height of two inches. Septa 

 unknown ; outer chamber deep. Siphuncle apparently dorsal. Surface of 

 cast marked by strong obliquely transverse annulations which become 

 gradually stronger from the concave side, and are gently curved back- 

 ward on the middle of the dorsum. Spaces between the annulations 

 concave, without any evidence of intermediate smaller ridges. Exterior 

 surface unknown, the specimen being a cast of the interior. 

 The figures referred to are the dorsal and lateral views of a fragment, 



with a transverse section. The accompanying outline figure shows the 



form of the entire cast of the interior, as nearly as can be given with 



materials in my possession. 



Formation and locality. In limestone of the age of the Niagara group, 

 at Bridgeport, Illinois. 



CYRTOCERAS (Phragmoceras.?) AMPLICORNE (n. s.). =^t<j>^'C^ t€r( 



PLATE 17 (8), FIGS. 6 & 7. \\!<.>*c.uie 



(Figures one-third less than natural size). '%( 



Shell large, strongly curved, making an entire volution, rapidly expand- 

 ing toward the outer chamber, which is less arcuate than the septate 

 portions of the shell ; transverse section broadly elliptical, becoming a 

 little flattened on the sides towards the outer chamber. 



Septa rather deeply concave and comparatively distant ; three of them, 

 measured on the dorsum, being nearly equal to the diameter of the 

 outer part of the largest one measured. The dorsal margins of the septa 

 are advanced so that a direct transverse section would cut the ventral 

 margin of the next preceding one. 



Siphuncle small, central or subcentral. Entire form of aperture unknown. 

 Surface finely striated, with the striae curving backwards to the dorsum. 



