Vol J, Grabau — Ordovician Fossils from North China (i) Go 



general weathered character of the surface, suggests the possibiUty that if more perfect 

 material were obtained, the longitudinal sculpture would be found to persist into the later 

 stages as discontinuous ridges in the interspaces. In that case the shell would be 

 referable to the genus Cycloceras. One might also argue, from the fact, that these fossils 

 are associated with Actinoceras, and other late Middle and early Upper Ordovician fossils, 

 that they belong more likely to Cycloceras, rather than to Protocycloceras, which is most 

 distinctive of the Lower Ordovician. Nor does the siphuncle help in the proper deter- 

 mination of the generic position of the form, as it is at present known only in section or 

 on the septal surface. The presence, in the largest fragment, of fine sharp concentric strias, 

 without indications of longitudinal striae, however, makes reference to Cycloceras doubtful. 

 Indeed this feature rather suggests Dawsonoceras, but the concentric striae are regular, 

 instead of being the frilled edges of the growth-lines as in that genus-. Such a surface 

 character has not been recognized in other Ordovician cephalopods, and it is possible 

 that we are dealing here with a new genus. However, as the material is too incomplete, 

 and as too little can be ascertained of tlie septa and the character of the siphuncle, it 

 seems best for the present to place the specimens in the genus Cycloceras, especially as in 

 species of that genus the longitudinal sculpture is not always preserved. 



Horizon and Localities: In the upper beds of the Actinoceras or Machiakou 

 limestone, in Limekiln Ravine, near Pei-tou-tze N.W. of Chaokouchuang, Kaiping 

 basin, Chihli. (Coll. Geo. B. Barbour) also in the same formation in other outcrops 

 near Chaokouchuang and Pei-tou-tze. (Collected by the Survey expedition). 



Suborder Cyrtochoanites Hyatt 

 Family LOXOCERATID^E Hyatt 



Genus SteREOPLASMOCERAS Grabau (gen. nov.) 



Non-annulated, regularly expanding orthoceracones with nummuloidal siphuncle, 

 the nummuli more or less irregular and extending from septum to septum, widest near 

 the centers of the camerae, but without secondary annular deposits, or if these are present, 

 they are irregular. Septa generally compound, or complicated by pseudosepta which 

 extend only partway across the phragmocone, and join the preceding or succeeding 

 septum. The space thus enclosed by the pseudosepta is commoaly filled with crystalline 

 stereoplasm deposited by the animal, this l)eing present in varying amount, sometimes 

 filling the whole or nearly the whole camera, especially in the older (earher) parts of the 

 phragmocone. 



