Nol I. Grabau — Ordovtcian Fossils jrom, North China (i) 75 



Most of the American Ordovician species occur in the Black River or early 

 Trenton formations, though some range down into the Stones River (late Chazyan), and 

 others up into the Galena hmestone (late Trenton) or even into the Cincinnatian. Their 

 geographical distribution ranges from the south central United States to the Arctic 

 regions. No species is known from the Ordovician of Europe with the exception of the 

 Scottish form noted, but the formation in which this occurs, is an extension of the North 

 American, not of the typical European Ordovician. * In the Silurian on the other hand, 

 this species is not uncommon in western Europe as well as in North America, and it 

 again occurs, though less abundantly, in the Lower Carboniferous (Mississippian or Di- 

 nantian) of these countries, though this may possibly be a distinct development of 

 Actinoceran characters in another genetic series. 



In China the genus appears to be practically confined to the northern provinces, 

 though Yabe describes and figures two fragments of undetermined species from Hsing- 

 shou Hsien, northwest of Ichang, Hupeh province. As the Ordovician of south China 

 is much better known than that of north China, and as these are the only fragment so 

 far obtained from the neighbourhood, though still to the north, of the Yangtze, it would 

 appear that the genus is unrepresented in the south of China. 



Actinoceras richthofeni Freeh 



Plate VII, figs. 1-3, Plate IX, figs. 4-8. 



191 1 Actinoceras richthofeni Freeh, in Richthofen, China, Vol. V., p. 8, Plate 11, fig. 4a (4b?) . 



This species was figured but scarcely described by Freeh, who merely states that 

 the siphuncle is subcentral in position and occupies about one-third of the diameter of 

 the shell. His illustration shows rather strongly concave septa about 3.4 mm. apart, 

 while the siphuncle has a fairly regular diameter of 14 mm. in the large end, which is 36 

 mm. in diameter, and 12 mm. in the smaller end, which is 20 mm. in diameter. The 

 distance between the two measured points is 46 mm., giving a rate of tapering of nearly 

 1 mm. in 3, though this is only approximate, as it is not certain that the section is 

 parallel to the axis of the shell. 



Shell oval in section, the two diameters being as 1 to 1.4 in the younger, and as 1 

 to 1.5 in the more mature portion; tapering at the rate of 1 in 3; or 1 in 3.5 laterally, but 



* Grabau loc. cit. The genus occurs on Bear Island and King William land, in the arc*ic region. 



