14 ART. 20. — M. YOKOYAMA. 



Most of the specimens are small, the largest complete one 

 (fig. 6) being 40 mm. in diameter with an umbilical width of 

 11 mm., and bearing about 58 ribs. There are however fragments 

 of larger shells which seem to have attained over 50 mm. in 

 diameter. A small specimen (fig. 5) 25 mm. in diameter has an 

 umbilical width of about 8 mm. and some 40 ribs. 



Locility : — Frequent at Nishi-Nakayama ; less so at Ishimachi. 



4. GRAMMOCERAS (?) OKADAI m. 



PI. IV. Fig. 3. 



We have a single specimen of a compressed, discoidal, keeled 

 shell, about 35 mm. in diameter and with an umbilical width 

 of about 10 mm. The whorls are laterally very flat, with a steep 

 umbilical wall and obtuse umbilical edge, and ornamented with 

 about 60 fine S-shaped obtuse ribs, separated by intervals of a 

 like breadth. The keel is sharp and bounded by shallow channels. 



This form resembles in its outer sculpture Grammoceras 

 acutum Tate (Wright, Lias Ammonites, pi. LXXXIL, fig. 7) 

 of the English Upper Lias, which seems to have more convex 

 lateral sides. 



Locality : — Nishi-Nakayaina. 



5. HARPOCERAS SP. 



PI. IV. Fig. 1. 



A flat, compressed, keeled shell, nearly 90mrn. in diameter, 

 with the umbilicus 24 mm. wide. The whorls are laterally flat- 

 tened and furnished with about 43 flat sigmoidal ribs, separated 



