JURASSIC AMMONITES FROM ECHIZEN A NAGATO. 7 



b3side the size of the shell, the whorls are rounder and the ribs 

 directed a little forward in the latter species. 



Locality : — Kaizara, in a dark micaceous shale. 



4. PERISPHINCTES (BIPLICES?) KOCHIBEI M. 



PI. I. Fig. 5. 



The single specimen, probably from Shimoyama, shows a 

 compressed, discoidal shell about 50mm. in diameter, with um- 

 bilical width of about 22 mm. The whorls are laterally com- 

 pressed and only very little convex, the umbilical wall being 

 almost perpendicular. The transverse ribs are numerous, radial, 

 generally rigid, elevated but obtuse, about 38 in the last whorl, 

 separated by intervals usually about twice as broad as the ribs 

 themselves, but sometimes less. These ribs bifurcate either at 

 half their lengths or a little higher up, and between the riblets 

 thus formed there is commonly a simple free rib, so that the 

 main ribs appear as if split into three. In a rare case the simple 

 rib reaches down to the edge of the umbilicus and assumes the 

 appearance of a, main rib with the intervals with the neighboring- 

 ones much narrower than in other cases. The shape of the 

 venter can not clearly be made out, but it seems to have been 

 more or less rounded. 



Suture-line unknown. 



Our species shows a close relationship to Perisphinctes triplex 

 Quenstedt and Perisphinctes polygyratus Re in ecke of the Oxford 

 formation. The main difference, if we set aside the shape of the 

 whorl which is at present uncertain, appears to be the irregularity 

 of ribs in the Japanese form. 



