506 PALAEONTOLOGY OF ILLINOIS. 



Genus PHRAGMOCERAS, Broderip. 



Phragmoceras Byronensts, Worthen. 



PI. 24, Kg. 6. 



Shell rather above the medium size and moderately arcuate, the sep- 

 tate portion of the shell as preserved in a cast in magnesian limestone 

 being about once and a half the depth of the chamber of habitation. 

 This outer chamber is ovate in outline, measuring 2.62 inches in its 

 dorso-ventral diameter, by 1.60 inch in a lateral direction, about 2 

 inches in depth and constricted at its junction with the septate portion 

 of the shell. The greater and lesser diameter of the septa are as 10 to 5. 

 Siphuncle rather large and close to the inner border of the shell. 



This species differs from P. nestor of Hall, (20th Eegents' Eeport on 

 the N. Y. State Cabinet, p. 405,) in the comparative size of its septa, 

 and more moderate curvature, as well as the form of its outer chamber 

 and position of its siphuncle. 



Locality and position : The specimen from which the foregoing 

 description was drawn was found at Kock Island, iu a block of Niagara 

 limestone evidently transported from the vicinity of Port Byron, 111. 



Genus CYRTOCERAS, Goldfuss. 



Cyrtoceras dardanus, Hall 1 



PI. 25, Pig. 6. 



Cyrtoceras dardanus, Hall, 1861, Report of Progress, Geological Survey of Wisconsin, p. 43, and 

 20th Kegents' Keport on the New York State Cabinet of Natural Hist., p. 406, PI. XVLT, fig. 3, 4, 5. 



" Shell robust, strongly curved, moderately expanding from the apex, 

 and slightly contracting near the aperture ; transverse section broadly 

 elliptical, the greater diameter iu a dorso-ventral direction. Dorsal and 

 ventral sides equally rounded; septa distant, measuring only four in a 

 distance equal to their transverse diameter, deeply concave and strongly 

 arched forward on the dorsum. The siphuncle of moderate size, dorsal." 



The above is the original description of this species, and our shell 

 appears to differ in the following characters : General form more robust, 

 not quite so strongly curved, septa not so strongly arched forward on 

 the dorsum, and apparently not so deeply coucave and measuring five 

 iu a distance equal to their transverse diameter. Not knowing to what 

 extent this form may vary, we place it provisionally under this spe- 

 cies. Should further comparison prove it distinct, it might. take the 

 name Cyrtoceras Fuitonensis. 



Locality and position : Pulton City, Illinois; in a buff limestone at 

 ike base of the Niagara, Upper Silurian. 



