CEPHALOPODA FROM THE HOKKAIDO. 23 



Gossan bed of the Alps, on comparison, has less involute whorls 

 (about i) and the ribs are less conspicuous. G. varagurense which 

 is allied to (r. ienuiUraium in the young stage of its shell, is a 

 species based on fragments from the upper Trichinopoly group of 

 Varagur, South India. It shows only one periodic rib in a space 

 corresponding to the last quarter of the last volution. 



The mature stage : — Whorls enlarging very rapidly ; rounded 

 and at the same time broadest at the umbilical edge, the breadth 

 from this point gradually diminishing toward the ventral side. 

 Involution more than i. Umbilicus narrow, very deep, surrounded 

 by a perpendicular wall. 



Surfoce with very narrow, sharp, prominent, simple, trans- 

 verse ribs whose greater part entirely surrounds the whorls. 

 Between the ribs, sometimes, shorter ones of the same character 

 are inserted. Interspaces between the ribs flat, measuring 2 mm. 

 on the ventral side. Periodic ribs composed of a partial 

 union of two ordinary ribs, with a regular interspace of about 

 2-3 cm. along the ventral side, 22 of which are on the last 

 volution of the largest well preserved specimen. 



The suture line is of the same type as in the preceding stage, 

 only it is very much complicated, the accompanying figure having 

 been taken from a large fragment found on the Bannosawa which 

 is, no doubt, considerably larger than that which the writer 

 has already referred to at the beginning. 



The full specific character is shown after the Ammonite 

 has attained its adult stage. The full grown shell is quite 

 different from others in form, while that of the young or middle 

 stage is very liable to be confounded with allied species. This 

 may be partly due to the fact that the adult shells of the allied 

 forms are mostly imperfectly known. 



