Vol I. Grabau Ordovician Fossils from North China (i) 63 



type), but it is difficult to see how it can be so regarded. It represents really an 

 Emloceran type in which the sheaths have assumed the form of tabulae separated by 

 interspaces, and as such rather supports the explanation of the relationship between the 

 endoshoaths of Holochoanites and the septa of Orthochoanites given above. Thus it is a 

 case of parallel development to Orthoceras, or the assumption, by the inner or true shell in 

 a holochoanitic type, of the orthoceran character. Unless we assume that the outer shell is 

 suppressed in the development of the Orthoceran type, we cannot regard this form as in 

 any way showing ancestral characters. Moreover, if such were the origin of Orthoceras, 

 the close genetic relation of the endosheaths of the one to the septa of the other type, 

 would be demonstrated. 



Suborder Orthochoanites Hyatt 

 Family CYCLOCERATID^E Hyatt 



Genus CYCLOCERAS McCoy 

 Cycloceras (?) peitoutzense Grabau (sp. nov.) 



Plate VI, figs. 1-4 



A number of fragments of an annulated orthoceracone have been obtained from 

 the upper beds of the Actinoceras limestone a short distance west of Chaokouchuang. 

 Although the} 7 belong to different individuals and show considerable variation in size, 

 they are nevertheless regarded as representing a single species. As this is the only 

 annulated orthoceracone known from north China, it will be described despite the 

 imperfect character of the material. 



The smallest shell fragment (PI. VI, fig. 1) is about 30 mm. long, the diameter 

 ranging from 5.3 mm. at the lower (partly concealed) end, to 7.2 mm. at the upper end. 

 Eight annulations are shown in a distance which is 23 mm. from the center of the first to 

 the center of the eighth annulation. The annulations appear to be straight, encircling 

 the shell without deflection, rounded, but separated by broad, strongly concave interspa- 

 ces which gradually increase in length with the growth of the shell. Very faint 

 longitudinal lines are visible upon the early portion of this fragment, but the greater part 

 seems destitute of them. Siphuncle somewhat excentric, its diameter at the upper end of 

 the fragment being 1.25 mm. Sutures and septa not visible. 



A second fragment (Plate VI, fig. 2) shows 7 annulations the distance between 

 the centers of the first and seventh being 20 mm. The diameter of' the shell at the 

 upper end is 12.2 mm. 



