^^^- ^- C. C. Y'li—Ordovician Cephalopoda of Central China (ii) 57 



Septa thin, having a concavity exceeding one half the depth of a camera. The 

 septa are 5 mm. distant from each other at the point where the longer diameter of the 

 shell is 14 mm., and gradually increase their interspaces tog mm. where the diameter 

 of the shell is 23 mm. 



Siphuncle central, being ovately eUiptical in section. Its major diameter measures 

 2 mm. at the smaller and 3 mm. at the larger end of the preserved fragment. At the 

 corresponding place the conch varies in its diameter from 16 to 26 mm. The sides of 

 the siphuncle are distinctly marked by the septal necks, which are a Httle longer than 

 one third the septal distance. 



Near the smaller extremity the camerse seem to have been separated horizontal- 

 ly into two nearly equal parts by a process directed toward the anterior angle on each 

 side of the camera. This feature is apparently similar to that seen in the specimen of 

 Orthoceras sp. Woodward. 



Another fragment of smaller size was also obtained. It has a length of 40 mm. 

 containing 11 camerte with an apical angle of 20°. The apex is more pointed and the 

 rate of tapering is more rapid, being 1:3. 



Compakion: This species closely resembles Orthoceras thomsoni Barrande \ but dif- 

 fers from it in the shorter septal distances, narrower siphuncle, and sub-elliptical sec- 

 tions of both the siphuncle and the shell. This form also bears some degree of 

 resemblance to Orthoceras sp.^ figured by Woodward, but the former has a more rapid 

 rate of tapering and a subelliptical section of shell. 



Horizon and Locality: In beds just overlying the blue thick-bedded limestone at 

 the western end of Pei-yang-shan, Chung-yang-hsien. The specific name is given in 

 honor of Dr. Y. C. Sun of the Geological Survey. 



Orthoceras elongatum Yu (sp. nnv.) 

 Plate VII., Fig. 5. 



This species is well shown in a natural polished longitudinal section. Shell 

 elongate, slender, and conical, having a length of 275 mm. The initial portion is point- 

 ed with an apical angle of 8°. It expands slowly toward the larger end. At a stage 

 262 mm. distant from the apex, it has a diameter of 22.5 mm. Rate of increase i in 14. 

 Cross section of shell circular. Body chamber and surface character unknown. 



1. Barrande: Syst. Sil. de la Boheme, Vol, II, Texte III, 1874, p. 684, pi. 214, figs. 4,5. 



2. Woodward: Quart. Journ. Gaol. Soc, Vol. XII, p. 378, pi. VI, fig. i. 



