18 ART. -2. — H. YABE : CRETACEOUS 



Geology of Japan : Descriptive Text accompanying the 

 Geological ]Map of the Empire. 



The writer proposes the following diagnosis by examining a 

 specimen with two volutions of the anterior portion of the shell 

 preserved. 



Shell dextral, narrowly elongated ; volutions widely apart 

 longitudinally ; umbilicus moderate in width. Whorls somewhat 

 obliquely elongated in cross-section. Surface ornamented with 

 numerous ribs aud also some periodic ones. Kibs strong, simple, 

 smooth and uniform, transverse and nearly straight on the external 

 surface of the whorls, curving gently on the inner upper margin 

 and thinning gradually inside ; intervals wide (about 2 ram. on 

 the average), smooth and flat. Periodic ribs very remote from 

 one another, one on two volutions, somewhat broader and much 

 higher than the other ribs. Septation unknown. 



It is by no means certain that the present species is specifically 

 distinct from T. indicus Stoliczka^^ The Indian species is 

 provided with volutions, contiguous when young and detached in 

 the advanced stage of growth with the ribs also nearly similar in 

 characters, the only difference l)eing in that the deeper periodic 

 furrows are bounded behind by a strong rib. According to 

 KossMAT,'-^ Heteroceras indicum is a species resembling H. poly- 

 plocihm Rœmek but distinguished by its constantly smaller size 

 and total absence of tubercles which often appear on the surface 

 of the whorl of //. jwlyplocum. 



F. M. Axderson"^^ referred a small form from Oregon, coiled 

 in a flat spiral, to //. indicum with query. The whorl of the 



1) Stoliczka : Cret. S. Ind., p. 184, pi. LXXXVI., figs. 1-2. Kossmat : Untsuch. ii. d. 

 siidind. Kreidef., \>. 14.'!, pi. XX., figs. 5 and 6. 



2) Kossmat: 1. c. p. 143: 



o) An-derson : Cretaceous Deposits of the Pacific Coast. 1902. P. 91, pi. III., figs. 96-97. 



