Vol. I. C. C. Yu — Ordovician Cephalopoda of Central China (ii) S9 



Comparison: At the first glance this species appears to show no difference from 

 Vaginoceras wahlenbergi Foord var. cylindrica, but on careful examination its elliptical 

 section and narrower size of the endocylinder as well as the absence ot stereoplamic de- 

 posit on the ectosepta give it a distinctive appearance. 



Horizon and Locality: From the argillaceous limestone of Neichiashan 

 formation at Chien-tze-kou {M 1- M), Nan-chang-hsien. (Coll. W. P. Shu and 

 C. C. Yii.) 



Vaginoceras neichianense Yu (sp. nov.) 

 Plate I., Figs, ga-b; Plate II., Figs. 6a-b, ya-b. 



General form subcylindrical, cross section elliptical, ectosepta crowded, endoconch 

 large, subcentral and circular in section. 



This is a fragmentary specimen preserving the septate portion. It is about loo 

 mm. in length. No external character is perceptible except the regular, transverse 

 ectoseptal edges exposed on the eroded surface of the cast. Rate of increase i in 8.5 

 approximately. The two diameters of the extoconch are roughly at the proportion 

 of 4:3. 



The ectosepta are closely set. The interspace between them slightly increases 

 upward, being equivalent to 1/5 the longer diameter of the ectoconch at the lower part 

 of the fragment and 1/6 at the upper. The concavity of the ectosepta is a little more 

 than the distance of one camera at its center. 



The endoconch is rather large, its diameter being nearly equal to 2/5 the longer 

 diameter of the ectoconch. It is situated a short distance from the center of the conch. 

 The continuous tubi extend apically to the point about one fourth the depth of the 

 next preceding camera, or a little more. The ectosepta are gently bent backward before 

 reaching the endoconch. The interior of the endoconch below the last endoseptum has 

 been changed into a white crystalline deposit. The endocone shows a slightly elliptical 

 outline in transverse section. Some camerse are filled with the calcite deposit, and 

 some ectosepta are also thickened by the stereoplasm to a very small amount. 



There are numerous specimens belonging to the same species, though they are 

 slightly different from one another. One specimen (Pt. II., Fig. 6) collected from 

 Chung-yang-hsien reaches a length of about 31 mm. It consists of four camera; 

 embedded in the red limestone. It tapers more rapidly, about 1:6. The endoconch is 

 relatively narrower, attaining a size of 1/3 the longer diameter of the ectoconch. 

 Ectosepta distant about '/^ the major diameter. 



