FOSSILS OF THE CARBONIFEROUS. 



265 



CEPHALOPODA. 



Genus ORTHOCERAS Breynius. 



Orthoceras Randolphensis Worthen T 



Plate xviii, tig. 1?. 



Orthoceras annulato-costatum Meek & Worthen, 1861. Proc. Acad. Nat. Sci. Philad., 

 vol. xiii, p. 147. Ibid., 1866. Geol. Illinois, vol. ii, p. 304, pi. xxiv, figs. 3a-b. 

 (Not Orthoceras annulato-costatum Boll, 1857.) 



Orthoceras Randolphensis Worthen, 1882. Bull. 111. State Mus. Nat. Hist., No. 1, p. 38. 

 By error in the Bulletin the original reference of this species is given as 

 Orthoceras annulo-costatum M. & W., 1862, Geol. Surv. 111., vol. vi, instead 

 of as above. 



With the means of comparison at hand the fragmentary remains of this 

 form from Nevada appear to be identical with those from the Chester lime- 

 stone of the Lower Carboniferous formation of the State of Illinois. The 

 most marked difference between them is the greater obliquity of the annu- 

 lations in the Nevada specimens, but this may be owing in a measure to 

 the crushing of the tube, which is compressed very much in all the examples 

 collected. 



Formation and locality. Lower portion of the Carboniferous limestone, 

 on the eastern slope of a small conical hill on the east side of Secret-canon- 

 road Canon, Eureka District, Nevada. 



Orthoceras Eurekensis, n. sp. 

 Plate xxiii, figs. 2, 2 a. 



Shell slightly curved. Transverse section broadly oval; the dorso- 

 ventral diameter the shorter, having a ratio of 7 to 8 with the lateral diam- 

 eter. Tube gradually and regularly enlarging. Chamber of habitation 

 unknown. Air-chambers have a depth of 4 mm where the dorso- ventral 

 diameter of the tube is 14 mm . Septa thin, smooth, moderately concave. 

 The suture has a broad retral curve over the dorso-ventral sides of the tube, 

 extending forward over both the lateral faces. 



Siphuncle small, slightly eccentric, and nearer the dorsal face of the 

 septum ; a narrow, flat areola surrounds it in the one section exposed to 



