Vol. I. C. C. Yu — Ordovician Cephalopoda of Central China (ii) 5S 



Comparison: This fragment may be correlated with Orthoceras chinense Foord* 

 and Orthoceras regidare Schlotheim^ but differs from the former in having much shorter 

 septal necks and from the latter in the more rapid tapering. So far as the visible 

 characters of this fragment are concerned, it may be assigned to the present species. 

 According to the description' given by Foord the siphuncle of M'Coy species is "central 

 in the young shell, but becoming eccentric with growth" and the surface is covered 

 "with fine transverse stride of growth". But the specimen in our possession only 

 represents the young stage, and the position of the siphuncle in the upper part as well 

 as the surface character are quite obscure. The specific identification of this specimen, 

 therefore, is made with a certain amount of hesitation. 



Horizon and Locamty: From the limestone bed of the Neichiashan formation 

 at Ta-hung-shan, Nan-chang-hsien. 



Orthoceras squamatulum Barrande. 

 Plate IV., Figs. 7a-b. 



iS68. Orthoceras squamatulum, Barrande: System Silurian de la Boh6me, Vol. II, Texte III, 1874 p. 

 455. Pl- 302, pi. 310. pi. 370. 



Shell straight, cylindrical, represented by a fragment of the posterior end, which 

 is 40 mm. long. Transverse section circular. It expands in diameter very gently, the 

 rate being about i in 30. The diameters at the two extremities of the fragment are 13 

 and 14 mm., while that of the siphuncle is 1.5 mm. wide throughout the whole portion 

 of the specimen. 



The septa are very shallow, about 1/3 the depth of the cameme. This fragment- 

 ary specimen contains four camersj, which have a depth of 2/3 the diameter of the shell. 

 In actual measurement the septa are 9 mm. apart at a diameter of 13 mm. 



Siphuncle slightly excentrir, narrow, being about 1/7 the diameter of the conch. 

 Cross-section circular. Septal necks clearly shown and extremely short. The cameras 

 consist of the same material as the surrounding rock. Test not preserved, but the sur- 

 face of the mould indicates that slightly oblique striae are present, four occupying a 

 distance of i mm. 



Comparison: Orthoceras michelini Barr.4 somewhat corresponds to the present 

 specimen, but Barrande's species has the septal distance much longer. Our shell is 



1. Foord: Catalogue of Fossil Cephalopoda, Pt. I, p. too. 



2. Foord: Catalogue of Fossil Cephalopoda, Pt. I, p. 5. 



3. Foord: Catalogue of Fossil Cephalopoda, Pt. I, p. 7. 



4. Barrande: Syst. Sil. de la Boh^me, Vol. II, Texte III, 1874, p. 642, pl. 221, pl. 3S1, pl. 

 442, pl. 447- 



