20 ART. li. H. YABE : CRETACEOUS 



and strong l)üt not seldom bifurcating and then weaker ; they 

 make a l)ackward curve on the lower marsjin and another forward 

 one near the upper, whei'e sooner or later they disappear. In- 

 tervals also not quite uniform, the breadth varying from 2 mm. 

 to o mm. Tubercles rather prominent, arranged in four rows of 

 which three are on the external side and one on the lower margin. 

 All the rows are equidistant from one another and parallel to 

 the suture except on the last portion of the shell in which they 

 are more or less oblique to the latter. Kibs, except weak and 

 short ones, bear a set of tul)ercles. 



Although this species agrees with T. cfr. Bergeri^^ in having 

 four rows of tubercles and transverse ribs, yet there seems to Ije 

 no further resemblance between the two. Helicoceras hystricvluiih 

 White'-' from the Cretaceous of Sergipe, South America, represents 

 a species probably belonging to the same type as ours. Excepting 

 this H. hystricuhuii, the writer is at present unaquainted with any 

 form which makes even a distant approach to the Japanese shell. 



Localities : — The Ikushumbets, Ishikari Pro v., the exact posi- 

 tion of the bed from which the specimens were derived is unknown. 

 But the (^tlier jMoUuscan remains found together in the same marly 

 nodule belong to the species common in the Pachydiscus-hQaa. 



NIPPONITES MIRABILIS gen. et sp. ^ov. 

 PL IV., tigs. 4-7 ; pi. VI., fig. 6. 



We have only a single specimen belonging to this entirely 

 new and extraordinary type of Ammonites. 



1) Vide supra. 



■1) WinrE: (jjutrihntions to the Paleontology of Brazil. 1888. P. 229, pi. XXII., figs. ?,, 4. 



