/^j\ 5g Palieontologid Sinica - ^^'>'- •^■ 



Septa gently concave, increasing in their distance from 3/4 to 4/5 the diameter of 

 the shell. At the stage where the shell is 11 mm. in diameter, the camera is 9 mm. in 

 depth, while at the uppermost preserved end the septa are 19 mm. distant from each 

 other,'being little less than the shell diameter which is 21 mm. at this place. Concavity 

 of septa approximately equal to one third the depth of a camera. 



Thesiphuncle is very shghtly eccentric, cylindrical, and very narrow. Its 

 diameter is about i/h that of the shell. The septal necks do not show very clearly, but 

 seem to be very short. The organic deposit is well developed along the margins of the 

 septa. 



Comparison: This form is characterized by its great septal distances. It comes 

 very near in aspect to Orthoceras currens Barrande,' but is differentiated from it by 

 the much narrower siphuncle, slower rate of tapering and much shorter septal necks. 

 The same characters in addition to the longer septal distance also distinguish this 

 species from Orthoceras chinense Foord. 



Horizon and Locality: This specimen was procured from the bed underlying 

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



Orthoceras densum Yu (sp. nov.) 

 Plate VI., Figs. 3a-b; Plate IX., Fig. 2. 



Shell cylindrico-conical with transverse section subcircular. Tube regularly 

 enlarging in diameter upwards. Apical angle about 8°. The larger extremity as well 

 as the surface character not observed. Tapering at the rate of i in 9. 



The cameras are extremely closely arranged in the apical portion, fourteen being 

 counted in a distance of 20 mm. commencing from the apex. They are six in number 

 in the next succeeding space of 20 mm. higher up. During the mature stage the earner* 

 greatly increase their depth, ranging from 10 to 17 mm., while the corresponding 

 diameter of the shell is from 14.5 to 20 mm. Near the upper end where the shell has 

 a diameter of from 20 to 30 mm., the septal distance scarcely increases, remaining about 

 16-17 mm. high. 



Septa smooth, thin, having a convexity nearly equal to one half the depth of one 

 camera, or a little more. Siphuncle narrow, central, circular in section, and apparently 

 enclosed by the septal necks which extend not less than one third the septal distance. 

 Its diameter is about 1/7 that of the shell. 



I. Barrande: Syst. Sil. de la Boheme, Vol. II, Texte III, 1874, p. 628, pi. 221, pi. 222, pi. 

 407, pi. 411. 



