(i) 48 



Palasontologia Sinica 



Ser. B 



surfaces of the siphuncle, as would naturally be the case in a structure which, as these 

 evidently did, rested upon the ventral surface. No specimen is however known with a 

 complete ventral surface, and the convergence is only shown by a slight obliquity upon 

 the sides. 



As indicative of the position of the specimens, it may be 

 noted that in one slab of rock, both sides of which were weath- 

 ered, and in which four specimens of C. nathani were found, 

 three, on the- same side of the slab, exposed the dorsal side 

 (Plate y. ) (this was apparently the upper surface of the slab 

 though sufficient care was not taken at the time of collecting to 

 determine this) while the fourth, on the opposite side of the 

 stratum (apparently the under side), exposed the weathered 

 ventral surface (Plate IV fig. 13). This slab was cut apart, 

 essentially parallel to the bedding plane, and the two cut 

 surfaces show the sections of the dorsal portion of the lower 

 specimen, these being shown in Plate II, figs. 11 and 12. The 

 position of the longitudinal axis of the lower specimen was 

 however approximately at right angles to that of the upper 

 specimens. 



Fig. 12. chihlioceras no- The remarkable character of the siphuncle warrants the 



thani. Diagrammatic longitud- . . 



inai section in the median plane Pacing of this genus into a distinct family, that, of the 

 along the line i-j. in fig. 7. CHIHLTOCERATID.E. The characters of this new family may be 



(Notation as in fig. 7. ) 



summarized as follows: 



Relatively short and stout holochoanitic othoceracones (and cyrtoceracones?) 

 with large siphuncle, generally divided by ehdosheaths, and filled with organically 

 deposited calcium carbonate. Final endosheath prolonged into a ventral blade, and 

 characterized by median and lateral endocones. Camera) unknown, but if present, 

 apparently as in Piloceras. Ordovician. 



Chihlioceras nathani Grabau (sp. nov.) 



Plate I fig. 10; Plate II, figs. 11, 12; Plate IV, fig. 13; Plate V; Text figures 2-13. 



Siphuncle beginning with a regular rounded end, characterized by a subcentral 

 mammillon with a large central scar, which marks the beginning of the endosiphuncle. 

 The expansion is rapid so that in the space of about l(i mm. from the apex (in the 



