Vo^- I- C. C. Yu — Ordovician Cephalopoda of Central China (ii) 6S 



Shell straight, annulated, with a slightly elliptical section. Owing to the moulds 

 not being well preserved the rate of tapering can not be precisely determined, but in 

 general the conch enlarges in diameter very slowly, about i in 20 or even less. Its 

 surface is encircled by coarse, concentric annulations, which are obHque to the axis of 

 the shell and nearly uniformly separated from each other. In some smaller specimens 

 they are distant about 5 mm., but in the larger ones the distance is 6 or 7 mm. from thd 

 summit of one ridge to that of the other. The obUque annulations are arched on the 

 opposite side to form broad saddles, which ascend about equal to the space separating 

 them. They occur as ridges with round edges. The interspaces between them are 

 concave and round. In one specimen (PI. VI., Fig. 5) the annulations and the 

 interspaces between them are again covered with very regular, fine strife, of which more 

 than ten are contained in a length of i mm. No longitudinal stri* are seen at all. 



The siphuncle is subcentral and slightly subcircular. It is nearer to the center 

 than to the side of the shell. Its diameter is 4 mm., where the shell measures 21 mm. in 

 minor diameter and 24 mm. in major. It occupies the position across the dorso-vientral 

 diameter and opposite the side bearing the broad saddles. 



RuMARKs: According to Reed's description' the rate of tapering is "at about i 

 in 40" and the annulations are "arched up strongly to form a broad high ventral saddle 

 on the siphonal side." I think that Reed only obtained one piece of the broken shell, so 

 the measurement of the tapering may be misleading. Regarding the siphuncle he 

 stated: "The position of the siphuncle is rather obscure", while our specimens indicate 

 the siphuncle lying at one side of the center just opposite the saddles. In any case our 

 shell is undoubtedly the same as Reed's species. 



Horizon and Locality: This species prevails in the upper part of the Neichiashan 

 near Sin-tan, western Hupeh. Many specimens were collected by J. L. Smith and 

 C. Y. Hsieh respectively. 



Genus CyCLOCERAS M'Coy 



Cycloceras sp. 



Plate VI., Fig. 6 



Shell straight, cylindrical, and annulated. Section unkown. Only a part of the 

 conch is preserved, being 23 mm. in length. Even though no test remains, yet the 

 surface markings may be examined on the surface of the internal mould. Siphuncle 

 and septa also unknown. 



I. loc. cit. 



