Vol. I. C. C. Yu — Ordovician Cephalopoda of Central China (ii) 35 



HoRizQN AND LocAMTiKs: The first two specimens (PI. Ill,, Figs. 2 and 3) were col- 

 lected by C. Li and W. P. Shu from the beds just below the red limestone near Ta-wu- 

 shu, north of the western end of Pei-yang-shan (^^ili), Chung-yang-hsien. The last 

 one (PI. II., Fig. 5) was collected by Mr. C. Y. Hsieh from the uppermost purple 

 calcareous shale of the Tafang limestone at Ta-fang village in the Yang-sing-district. 



Vaginoceras peiyangense Yu (sp. nov.) 

 Plate v., Figs. la-b, 2a-b. 



This orthocone is fairly slender, elongate, reaching a length of 425 mm. The 

 ectoconch terminates in an extremely acute point. It enlarges in diameter very slowly 

 in the young part, but rapidly toward the apertural portion. The diameter of the 

 ectoconch increases from 15 mm. at the lower part to 30 mm. at the upper, the distance 

 being 289 mm. This gives a rate of expansion of i mm. in 19 mm. The remaining 

 part of the living chamber is rather long, having a length of 60 mm. and a diameter of 

 about 30 mm. at its base. Aperture not observed. The section of the outer shell is 

 ovately elliptical with a moderately large endoconch close to the margin of the shell. 



The ectosepta are very thin and gently concave. Their depth is about one half 

 that of a camera. The ectoseptal interspaces or camerae regularly increase in height 

 toward the aperture, there being three camerte in the space of 20 mm. at the apical 

 portion and one camera or a little more in the same space at the stage next to the body 

 chamber. 



The endoconch is tubular, moderately large with an oval section. It measures 6 

 mm. in major diameter and 4.5 mm. in minor. In the same stage the transverse 

 diameter of the ectoconch is 26 mm. It hes rather close to the outer shell, if it is not 

 absolutely in contact with the latter. It is comparatively flatter on the ventral side. 

 At a point 150 mm. from the apex, we find in section that the subtriangular endocone 

 exists within the endoconch having an apical angle of nearly 17°. The endoconch of 

 the earher stage is solidly filled with the calcite deposit, leaving the endosiphotube 

 'open in the middle. Its diameter is more than o.i mm. and is plainly visible even to 

 the naked eye. The endoconch is provided with the tubi, which continue apicad beyond 

 the next preceding ectoseptum for a short distance further. 



In another specimen (PI. V., Fig. 2) the camerne of the ectoconch are relatively 

 shallower. The ectosepta regularly and slowly increase their distance upwards, varying 

 from 5 mm. to 7 mm., where the corresponding width of the ectoconch is from 13-18 mm. 



