^ol. I. C. C. Yii — Ordovician Cephalopoda of Central China (ii) 3S 



Another individual (Plate IV., Fig. 2) is also known from a fragment of more 

 than one hundred and thirty millimeters in length. The camerte of the ectoconch 

 increase their depth forward at a regular rkte, ranging from 9 to 13 mm., where the 

 corresponding diameter of the ectoconch is from 27-35 mm. Endocylinder circular, 

 marginal, large, being about 2/7 the diameter of the ectoconch. Concavity of ectosepta 

 about 2/3 the camera. The outer shell tapers at the rate of i in 12.5. The organic 

 stereoplasm deposit is seen on the under side of the ectosepta more commonly than on 

 the upper. 



Comparison: This form is closely related to Vaginoceras wahlenbergi Foord, from 

 which it may be slightly distinguished by the more regular increase of the ectoseptal 

 distance and the smaller size of the endoconch and endocy Under. According to the 

 diagnosis given by Foord, Vaginoceras wahlenbergi has a much larger endoconch, 

 measuring "nearly half the diameter in the young shell" and "about one third the 

 diameter" in the adult. Nevertheless, the other important characters of our shell are 

 very similar to those of Foord's species, it is, therefore, preferable to refer it to a 

 variety of Vaginoceras wahlenbergi. 



Horizon and Localities: One specimen (Plate IV., Fig. 2) was found just below 

 the thin-bedded red limestone in the vicinity of Liu-chia-sze south of Cha-ti-pu, Hsien- 

 ning-hsien, and another specimen (Plate IV., Fig. i.) was from the same formation near 

 He-chiao, Chung-yang-hsien. (C. Li and W. P. Shu Coll.) 



Vaginoceras endocylindricum Yii (sp. nov.) 

 Plate II., Figs. 5a-c; Plate III., Figs. 2a-d, 3a-b. 



This specimen (PI. III., Figs. 2a-d) is known by a large orthocone 

 which attains a length of 280 mm. with a slender obtuse termination at the apical 

 end. The section of the ectoconch is circular. Its diameter measures 42.5 mm. at 

 the larger end, and 145 mm. at the smaller. It tapers at the rate of 1:9.8. Owing to 

 the imperfection of the upper end of the specimen the original size of the living chamber 

 has not been fully determined. Nevertheless, the length of its remaining part is more 

 than twice the diameter of its base. 



The ectosepta are rather closely set. Their convexity attains nearly the depth 

 of one camera. The ectosepta are 5 mm. apart near the apical end and increase re- 

 gularly slightly forward. There are three camerre in the space of 20 mm. in the mature 

 part of the phragmacone, where the ectoconch has a diameter of about 23 mm. Near 

 the living chamber, the ectoseptal interspace is 9 mm. at the diameter of 35 mm. 



