Vol. I. C. C. Yu — Ordovician Cephalopoda of Central China (ii) 59 



Another small specimen (PI. IX., Fig. 2) of the same species was found. Its 

 body chamber has only a small part of the base preserved. It gradually decreases in 

 diameter apicad, to an acute point with an apical angle of 10''. Rate of increase i in 

 7.5. The septa at the smaller end are very numerous, being more than 10 camerte 

 within the length of 20 mm. After the rapid increase of the septal distances in the 

 middle part of the conch, the cameme apper to be retarded in the rate of increase in 

 depth as compared with its diameter. Near the larger extremity where the diameter is 

 13 mm. the septa are distant about 7 mm. 



Rkmarks: This species is distinct from any of the preceding ones in its extremely 

 crowded camene at the apical portion and the irregular increase of the septal distance. 

 I have not found any related form, with which this species may be identified. 



Horizon and Localities: One speciemen (PI. VI., Fig. 3) was obtained from the 

 upper part of the Neichiashan formation at Chien-tze-kou about 3 li to the west of Nan- 

 chang-hsien, and the other (PL IX., Fig. 2), from the same bed at Liu-chia-chung (fij^^if ) 

 about 15 li west of Kueng-chia-wang, I-cheng. 



Orthoceras yangtzeense Yii (sp. nov.) 

 Plate III., Figs. 7, 8a-b. 



There are three specimens of internal moulds which are cylindrico-conical and 

 slightly curved. The cross section is elliptical, its two diameters being at the ratio of 

 3:2. Its tapering is rather rapid, about i in 6. Larger extremity not preserved. 



It is to be noted that the septal sutures are slightly undulating and form on the 

 convex side the V-shaped lobes, which are very characteristic of this species. The 

 septal distances are very uniform and are about three millimeters apart on the average, 

 while the longer diameter of the shell is 8 mm. at the lower end and 14 mm. at the 

 upper end of this fragment, which is little less than 40 mm. in length. 



The position of the siphuncle is rather uncertain. But the upper end of one 

 specimen (PI. III., Fig. 8) shows that it is small, circular, submarginal to the shell wall 

 opposite the side which bears the V-shaped lobes. 



Comparison: In the closer septa and the V-shaped lobes the present species 

 somewhat resembles Orthoceras sp.^ figured in Angelin-Lindstrom's Fragmenta Silurica. 

 Since no description of that form was given, we are not able to malce any accurate 

 comparisons . 



I. Angelin-Lindstrbm: Fragmenta Silurica, t. IV. fig. 16. 



