2 ART. 2. H. YABE : CRETACEOUS 



Soon after D'Orbigny, Quenstedt^- considered the separation 

 of Helicoceras from Tunnlites quite unnecessary, while Sharpe^' 

 and Stoliczka'^^ were of opinion that the so-called group of T. 

 7'otundaü should be brought under the genus Helicoceras, retain- 

 ing the name Tiirrilites only for the T. cmc/ulaii of D'Orbigky. 

 Pjctet/^ however, proposed to divide Helicoceras into two groups, 

 the one having a short spire and widely separated volutions and 

 the other showing a high s^iire and less Avidely separated volutions. 

 The first of these groups he called Helicoceras proper, while the 

 second as well as the group, T. roiundati, were considered by him 

 to be distinct genera. 



Meek'*^ like D'Orbigny took Helicoceras in the most restricted 

 sense and divided it into Helicoceras proper, Patoceras, and 



Canada on the one side, and those of tlie Hokkaido on the other. A discussion of these, 

 however, the writer intends to put forth in the last part of this work. 



As to the new fossil localities in the Hokkaido, no important addition to our know- 

 ledge has been made during recent years ; but several new forms have been brought back 

 by geologists who have lately visited the localities already known. Among these, the writer 

 Avould mention a valuable collection made by Prof. Yokoyajnia at Urakawa, a locality 

 that had not been visited by geologists for more than twenty years. 



During the last four years, the writer has devoted mucli time to the study of- the 

 morphology of the Hokkaido Ammonites, and has also taken the opportunity of making 

 himself acquainted with the development of several of tiieir predominating types, for it has 

 now become clear that a mere morphological study of adult specimens is not sufficient for 

 the establishment of their real affinities, and that by the study of their development only 

 can such knowledge attained. Consequently, the result obtained from this side of the be 

 study is also occasionally embodied in the following descriptions. 



In this second part, the following genera are described : — 



1) Turrilites, Helicoceran, Uderoccras and Nip-ponitci<. 



2) Olcostcplianus. 



'.'>) Desnto<;er((s and Jlauericcms. 



There is also one species whose generic position is still undetermined. 



The order in which tlie different groups are here treated is not due to the jiresence of 

 any mutual relations existing among them but merely for the sake of convenience and of 

 avoiding too long a delay in the ])ub]ication of the paper. 



1) Quenstedt: Petrefaktenkimde Deutschlands. I. Ceplialopoden. P. 297. 



2) Sharpe: Mollusca of tlie Ciuilk. P. 59. 



3) Stouczka : I.e. p. 18;{. 



4) Pictkt: Paléont. Suiss. Foss. de Ste. Croix. P. ]20. 



0) Meek: Invert, ('ret. and Tort. Foss. of the Fjipcr Missouri Comity, p. -IS-"). 



