^'o/. /. C. C. Yu — Ordovician Cephalopoda of Central China (ii) 43 



The ectoseptal distances are nearly uniform, varying from 5-6 mm., or about 1/5 

 tlie longer diameter of the ectoconch. Ectosepta with a concavity nearly equal to the 

 depth of one camera. 



The endoconch is elliptical in section., being about 9.5 mm. and 8 mm. in its two 

 diameters. At the same section the ectoconch measures 32 mm. in its major diameter. 

 Tapering of endoconch very gentle. The continuous tubi are disposed in an imbricating 

 arrangement. The endosepta are hardly visible in the stereoplasmic filling. The empty 

 camene are lined with slight organic deposit, which occurs on the upper side of the 

 ectosepta in the majority of cases. 



The ectoconch gradually contracts from the longer diameter of 30 mm. at the up- 

 per extremity of the specimen to 23.5 mm. at the lower. The tapering may be roughly 

 estimated to be at the rate of i in 11 mm. 



Another fragment of this species (PI. II., Fig. g) was obtained from the same 

 district. It is of smaller size. The ectosepta are also crowded, distant about 3-4 mm. 

 from one another. The longer diameter of the ectoconch measures 16 mm. at the lower 

 part and 20 mm. at the upper. Concavity of ectosepta about i camera. The elliptical 

 endoconch lies submarginal to the outer shell. The stereoplasmic deposit usually 

 occurs above the margins of the ectosepta in very small quantity. Neither the earlier 

 portion nor the apertural end have been observed. 



The third one (PI. V., Fig. 4) was collected from the upper part of the Tafang 

 limestone at Yang-sing-hsien. Its transverse section is also elliptical in outline, the two 

 diameters being at the ratio of 3:2. The ectosepta are uniformly distant from one an- 

 other, attaining an interval of 6.5 mm. in average, or about 1/4 that of the longer 

 diameter. Endoconch marginal, elliptical, being about 1/3 the diameter of the ecto- 

 conch. So far as we know, this specimen is slightly differentiated from the preceding 

 ones in the position of the endoconch, which hes not across the minor diameter but at 

 the quadrant between the longer and shorter diameters. 



Comparison: In the position of the endoconch, section of the ectoconch, and the 

 rate of tapering this species may be compared with Endoceras arctiventrum Hall' from 

 the higher part of the Trenton limestone near Middleville N.Y., but the enloconch of 

 Hall's form is much smaller in size. Our shell has the long invaginated tubi, which are 

 unknown either in the figure or the description of that form given by Hall. 



Horizon and Looalitiks: The last named specimen (PI. V., Fig. 4) collected by 

 C. Y. Hsieh was from the upper red_ bed of the Tafang limestone at Yang-sing, and the 

 rest from the red limestone at San-shan-yuan, Chung-yang-hsien, (C. Li and W. P. Shu). 



I. Hall: Palaeontology of New York, Vol. I, p. 217, pi. 51, figs. 2 a,b. 



