^ol. I. C. C. Yu — Ordovician Cephalopoda of Central China (ii) 49 



greater diameter of shell than the original maximum width. The camera; are filled with 

 the fine yellow matrix of calcilut5'te except the initial portion, which has turned into 

 calcite. 



Comparison ; This form agrees in all respects with Orthoceras chinense Foord, but 

 differs slightly in having shorter septal necks, longer septal distances and the gradual 

 increase of camera depth towards the aperture, these features serving to separate it as a 

 variety of Foord's species. It may be compared with Orthoceras evanescens Barrande', 

 but is easily distinguished by its more rapid tapering, its surface ornamentation, 

 its broader siphuncle and the regular increase of its septal distance. Orthoceras penetrans 

 Barr.2 and Orthoceras cavum Barr.3 also come nearer to this form in general aspect, but 

 our shell has longer septal necks and surface striation, which are very different from 

 those of Barrande's species. It is also allied to Orthoceras gieheli Barr.4, but that shell 

 has different surface ornamentation and longer septal necks. 



Horizon and Localities: The specimen (PL VII., fig. i.) is from the same 

 formation as the preceding species in the region about i li to the east of Chiang-chia-chi 

 (# ^ M), and about 10 li north east of Kuang-chiao-pu, King-shan-hsien. (W. P. Shu 

 and C. C. Yii). The last specimen (PI. VII., Fig. 2) was obtained in the bed between the 

 reddish limestone and the thick-bedded blue limestone at the place close to Wang-chia- 

 sze, Chung-yang-hsien. (C. Li and W. P. Shu). 



Orthoceras chinense var. eccentrica Yii (var. nov) 

 Plate VIII., Fig. 2. 



Shell cylindrico-conical, regularly enlarging.' Transverse section circular. Cham- 

 ber of habitation not perfectly preserved. This specimen is about 210 mm. in length, 

 measuring 40 mm. in diameter at the larger extremity. The apex terminates in an acute 

 point with an apical angle of 25°, but this is probably not the true angle as the apical 

 portion is displaced by faulting and the section not wholly median. The normal rate of 

 tapering of the shell may be estimated at i in 7. Surface markings unknown. 



1. Barrande : S3'steme Silurien de la Boheme, Vol. II, Text III, p. 190, pi. 258, pi. 265; pi. 

 326, pi. 361. 



2. J. Barrande : Systeme Silurian de la Boheme, Vol. II, Text III, p. 537, pi. 403, pi. 406. 



3. J. Barrande : Systeme Silurian de la Boheme, Vol. II, Text III, p. 488, pi. 223, pi. 363, 



pl. 378. Pl- 384- 



4. J. Barrande : Systeme Silurian de la Boheme, Vol. II, Text III, p. 404, pl 304. 



