(I) 48 



raLrontulogia Sinica 



Ser. B 



surfaces of the siphuncle, as \\'ould naturally Le 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 G. nathani were found, 

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

 (Plate V.) (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 weathei-ed 

 ■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. 



The remarkable character of the siphuncle warrants the 

 placing of this genus into a distinct family, that of the 

 Chihlioceratid^. The characters of this new family may be 

 summarized as follows: 



Fig. 12. Chihlincrax iin- 

 Ihnni. Diagrammatic longitud- 

 inal section in the median plane 

 along the line / - J. in fig. 7. 

 (Notation as in fig. 7. ) 



Relatively short and stout liolochoanitic othoceracones (and eyrtoceracones?) 

 with large siphuncle, generally divided by- endosheaths, and filled with organically 

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

 characterized by median and lateral endocones. Camera3 unknown, but if present, 

 apparently as in Plloccras. Ordovician. 



Chihlioceras nathani Grabau (sp. nov.) 



Plate I fig. 10; Plate II, figs. 11, 12; Plate IV, fig. 13; Plate V; Text figures 213. 



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

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

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



