CEPHALOPODA FROM THE HOKKAIDO. 39 



The occurrence of Desmocerai Dmusoni in the Cretaceous of 

 the Hokkaido is of special importance, as among the few Japa- 

 nese forms which show some reUition to those of the North 

 American Pacific species, none is more closely related than the 

 present one, and it is also a remarkable fact that a bivalve, 

 very much like Thetis affinis Whiteaves'' from the C horizon 

 of the Queen Charlotte Islands is found abundantly together 

 with this Ammonites in the same layers. 



Locality and horizon : — Several specimens of this Ammonites, 

 one of which is here figured, were obtained along the Ikushum- 

 bets 10 miles east of the Ikushumbets coal mines, Ishikari 

 Prov. Up to this time it has been met with only at the above 

 locality where it is quite numerous in a sandstone of the Thetis- 

 zone, associated with Thetis aff. affinis Whiteaves. 



DESMOCERAS PORONAICUM m. 



PL VL, figs. 1, 2. 



Dimensions : — 



Shell small, discoidal, composed of a few compressed whorls, 

 which are nearly parallel sided and slope gradually to the round- 

 ed ventral surface. Involution very deep ; umbilicus narrow 

 with the perpendicular wall, exposing only a very small portion 



1) Whiteaves: Mes. Foss. vol. I., pt. 3, p. 226, pi. XXX., tigs. 4, 4a, b; pt. 4. p. 290. 



