4 AKT. 20. — M. YOKOYAMA. 



tolerably sharp in the inner whorls, but become gradually obtuse 

 towards the mouth. They rise at the umbilical suture, are 

 directed a little forward and divide into three smaller ones near 

 the venter into which they seem to pass in a straight line. In 

 the last and the next to the last whorls, there are two deep 

 grooves which are more oblique than the ribs and separated 

 from each other by about one-half the length of the whorl. 



The diameter of the shell in our only specimen is 138 mm. 

 with an umbilical width of about 77 mm., so that the ratio of 

 the two is 10 to 5,7. But as the specimen is somewhat distorted, 

 the real umbilical width may be a trifle less. 



The number of ribs in one half of the last whorl is 28, so 

 that the whole number may be about do. 



The suture line seems to be deeply incised, although it is 

 not distinctly visible. 



This species shows a great resemblance to Perlsphincies pro- 

 miscuus Bukowski {lieber die Jurabildungen von Czcnslochau in 

 Polen, p. 308, pi IV., fig. 1, pi V., figs. 1, 2) of the Lower 

 Oxford of Poland. The only difference which I could find in the 

 surface markings of the two is in the number of ribs which in the 

 Polish species is said to be 50. The shape of the whorls can not be 

 well compared, as our specimen has been subjected to rock-pressure; 

 but as far as I can judge from the general outline of the shell, the 

 Japanese form appears to have a laterally more compressed whorl 

 than the Polish one, in which it is said to be ovate in section. 



Perisphinctes promiscuus occurs also in the Lower Oxford 

 of France and Portugal. 



Locality: — Nagano, in a hard dark- coloured shale. 



