^'^^ ^- Grabau — Ordovician Fossils from North China (i) 89 



known from these rocks. The species is placed in the genus Adinoceras rather than 

 Cyrladinoceras, because of its shght curvature, moderate tapering, and large actinoceran 

 siphuncle. Another smaller specimen with narrower siyhuncle (9 mm. where shell is 15 

 mm. wide), but otherwise similar, and also showing shght curvature, has been obtained 

 from the same horizon, south of Wen-Nan, Mon-Yin-Hsien, Shantung. (V. K. Ting 

 coll.) 



Genus CyrtacTINOCERAS Hyatt. 



This genus, founded by Hyatt, with Cyrtoceras rebelle Barrande as the genotype, 

 was more fully defined by Euedemann (N. Y. State Museum Bull. 90, 1906, p. 488), who 

 referred to it two species from the Chazy limestone (Middle Ordovician) of the Lake 

 Champlain region in eastern North America. They are rather short and stout cyrtocera- 

 cones with highly nummuloidal siphuncle, characterized as in Adinoceras, by stereoplasm 

 which is arranged as obstruction rings or "rosettes" around the septal necks. The 

 camerae too are tilled with stereoplasm, this being very extensive in one of the Chazy 

 species. In the type of the genus, the section is depressed, the septa rather closely 

 arranged, the siphuncle moderately nummuloidal shrinking somewhat in old age, and 

 filled in the middle stages with rosettes. It is near the convex side of the conch, but 

 somewhat variable in position, approaching the center again in old age (Euedemann). 



From curved forms of Adinoceras the species of this genus may be distinguished 

 by their rapid enlargement, this producing relatively short stout shells. The siphuncle of 

 the curved Adinoceras species is also much larger in proportion than is that of Cijrt- 

 adinoceras. 



Cyrtactinoceras frechi Grabau (sp. nov.) 



Plate VIII, figs. 7-10. 



Shell a comparatively small breviconic cyrtoceracone of subcircular or somewhat 

 oval section and gentle curvature, the shorter of the two transverse axes in the plane of cur- 

 vature. The shell tapers at the rate of 1. in 2.5 in the early stage, having a transverse 

 diameter of 10 mm. at the second septum, below which it is rounded off acutely. Seven- 

 teen millimeters above the second septum it has a transverse diameter of 18 mm. while the 



