Vol. I. C. C. Yii — Ordovician Cephalopoda of Central China (ii) 55 



Orthoceras remotum Yu (sp. nov.) 

 Plate VII., Figs. 4 a-b. 



Shell slender, elongate, cylindrical. Transverse section elliptical. It tapers very 

 slowly, about i in ig. The fragmentary specimen has a length of 225 mm. embracing 

 10 camerse. The two extremities have not been observed. 



Septa strongly concave and very distant from each other. Their concavity is 

 nearly equivalent to two fifths of the interspace between the septa. The camerse 

 regularly increase in depth as the shell expands in diameter, measuring 18 mm. in the 

 smaller portion and 26 mm. in the upper, while the shell is 21 mm. and 29 mm. in dorso- 

 ventral diameter respectively. The obliquity of the septal lines makes an angle of 70° 

 with the median axis of the siphuncle and meets the side of the shell at 40*. 



The siphancle is strongly excentric, being 9 mm. distant from the nearer side of 

 shell at the upper end and 6 mm. at the lower. It is narrow and elliptical in cross sec- 

 tion. Its major and minor diameters are 3.5 and 2.5 mm., while the corresponding 

 diameter of the shell are 30 mm. and 23 mm. respectively. The septal necks are not 

 clearly exposed, but at the smaller end they may be perceived to have a very slight 

 length. 



Test smooth, being 0.5 mm. in thickness. 



Comparison: This species is characterized by the strong concavity of its septa 

 and the great depth of its camerse. It may be compared, with Orthoceras pleurotomum 

 Barrande' and Orthoceras thyrsus Barrande,^ but is readily distinguished from the latter 

 by the great septal distance, the elliptical section of shell and the absence of the sur- 

 face ornamentation; and from the former by the fact that the shell is covered by delicate 

 oblique striations, while the septal intervals become crowded upwards. 



HoKizoN AND Locality: It occurs in a polished slab collected from the upper bed 

 of the Neichiashan formation at Chai-tze-shan (|g^ilj) about 10 H south of Fang-chia- 

 chi [-^m.^)' Hsiang-yang-hsien (|g|^!lj). 



Orthoceras rudum Yu (sp. nov.) 

 Plate IV., Figs. 8a-c. 



Shell straight, cylindrical, enlarging very slowly. Transverse section sUghtly 

 elliptical. In this imperfect specimen only the basal portion of the body-chamber is 

 preserved together with three adjacent ordinary camerae. The entire length of the 

 fragment is 70 mm. The rate of increase may be computed as 1 in 20. 



1. Barrande: Syst. Sil. de la BohSme, Vol. II, Texte III 1874, p. 412, pi. 224, pi. 296, 



pi. 366. 



2. Barrande: Syst. Sil. de la Boheme, Vol. II, Texte III, 1874, p. 555, pi. 405, figs. 15-18. 



