(ii) 52 Palxontologia Sinica Ser. B. 



Orthoceras regulare Schlotheim. 



Plate IV., Figs. 5, 6 a-b. 



1888. Orthoceras regulare, Foord: Catalogue of Fossil Cephalopoda, Part I, p. 6. (With literature 



references). 

 1917. Orthoceras regulare. Reed: Palfeontologia Indica, New Series, Vol. VI, Mem. No. 3, p. 32, pi. 

 V, figs. 13, 13a. 



There is a small shell which can be identified with this species. The larger 

 portion has not been observed and the part remaining attains 45 mm. in length. It is 

 straight and cylindrical in general form and subcircular (probably compressed) in cross 

 section. Rate of increase about i in 15. Septa strongly concave and separated from 

 each other a distance of about 1/2 the diameter of the shell. Depth of the septa 

 exceeding 1/2 that of the camera. Siphuncle central, circular, being about 1/9 the shell 

 diameter. It is distinctly girdled by the septal necks, which are extremely short. The 

 white calcareous deposit is present in the camerse, but not in the siphuncle. No test 

 remains, but the surface of the mould seems to be transversely striated. In another 

 specimen (PI IV,, Fig. 6) the shell has a circular section, tapering at the rate of i in 18. 



Comparison: In the septal distances and the position of the siphuncle, the 

 present shell is somewhat close to Orthoceras chinense Foord, but our shell has the septal 

 necks much shorter and the tapering much slower, features readily distinguished from 

 those of Orthoceras chinense. 



Horizon and Locality: Embedded in the upper limestone bed of the Neichia- 

 shan for'mation, near Sin-tan (C. Y. Hsieh Collector). 



Orthoceras cf. politum M'Coy 



Plate III., Fig. 6 



1888. Orthoceras politum, Foord: Catalogue of Fossil Cephalopoda, Pt. I, p. 7. (With literature 

 references). 



Shell straight, slender, embedded in the yellowish argillaceous limestone. Only 

 the apical portion is recognized, with six camerre remaining. The cross section is circular. 

 Because the longitudinal section is obhque to the axis of the shell, the siphuncle is only 

 partly exposed at the upper end. It tapers at the rate of i in 10. The distance between 

 the septa sHghtly and gradually increases upwards, ranging from 2/5 the diameter at the 

 lower end to 1/2 at the upper end of the fragment. Depth of septa about 1/4 the shell 

 diameter. Siphuncle circular, central, having a diameter about 1/7 — 1/6 the diameter 

 of the shell. Septal necks extending less than 1/4 the depth of the camera. The surface 

 markings of the test are unknown. 



