Vol. I C. C. Yu--Ordovician Cephalopoda of Central China (n) 45 



Vaginoceras giganteum Yii (sp. nov.) 

 Plate III, Figs. 4 a-b. 



Ectoconch straight, robust, cylindrical, enlarging very slowly. Endoconch rather 

 large. As both the ectoconch and endoconch are much eroded, their cross sections are 

 not quite certain, though they are probably circular. The apical portion is missing and 

 the length of the incomplete body-chamber also can not be fully determined. This 

 fragment has a length of 360 mm. comprising fourteen camerte. At the two extremities 

 it measures 67.5 and 48.5 mm. in diameter. It expands at the rate of i in 18.5. 



Ectosepta thin, moderately concave, appearing much thickened on their upper 

 marginal portion by the stereoplasmic deposit. They are distant from each other about 

 one half the diameter of the ectoconch. Their concavity is about three fourths as deep 

 as the camera. It is a noticeable fact that the ectoseptal distances are almost equal 

 throughout the whole fragment. There are two cameras within the space of 50 mm. 



The endoconch lies ventro-centran. It is of large size, a little less than one third 

 the diameter of the ectoconch. It is slightly contracted between the ectosepta. At the 

 lower part of the fragment the endoconch is distant 11 mm. from the ventral side of the 

 outer shell and 25 mm. from the dorsal, where the diameters of the ectoconch and endoconch 

 are 52 mm. and 16 mm. respectively. It is only preserved in the lower portion and the 

 upper end of the specimen, and the rest is completely worn away. The uppermost part 

 of the endoconch encloses another smaller orthoceracone 10 mm. long. All the camerae 

 and the lower part of the endoconch are wholly filled with calcite deposit. No endosepta 

 are seen, but the presence of the imbricating tubi and the enormous endoconch shows 

 that this specimen should be referred to the genus Vaginoceras. 



Comparison : This species may be related to Vaginoceras wahlenhergi Foord, 

 but differs from that in the slower rate of tapering, equal ectoseptal intervals, and 

 position of the endoconch. The same features also serve to differentiate this form from 

 Vaginoceras wahlenbergi Foord var. cylindrica. 



HoKizoN AND Locality : Obtained from the fossiliferous bed underlying the red 

 limestone near Ta-wu-shu, Chung-yang-hsien. 



Vaginoceras? sp. 



Plate VIII., Fig. i. 



This specimen consists wholly of the red lime matrix, in which the shell was 

 embedded. It has a length of about 400 mm. On the surface of the stone nucleus the 



