JURASSIC AMMONITES FROM ECHIZEN & NAG A TO. 11 



formation which undoubtedly belongs to the Lias, and indeed to 

 its upper part. 



There seem to be several horizons in the Ammonite-bearing 

 layers. Mr. Inouye speaks of three such as existing at Nishi- 

 Nakayama, while Mr. Okada mentions only two from Ishimachi. 

 It is to be hoped that future investigations will throw more 

 light on this subject. 



DESCRIPTION OF THE SPECIES. 



1. HILDOCERAS CHRYSANTHEMUM M. 



PI. II. Figs. 1-4. 



The shell is diseoidal, very much compressed, carinated and 

 widely umbilicated, with the umbilical wall very steep or nearly 

 perpendicular. The whorls are narrow and only very slightly 

 involute, with lateral sides fiat and furnished with numerous, 

 broad, obtuse, sigmoidal ribs separated by valleys of a like breadth. 

 These ribs become flatter and less prominent toward the mouth, 

 and where they bend backward, which takes place at about à 

 their length from the umbilical edge, the surface of the whorl is 

 marked by a shallow depression which is most distinct in the 

 last half of the last whorl. Body-chamber about I. The external 

 saddle is broader than the external lobe, and divided into two 

 unequal parts by a shallow incision ; the external lobe is quite 

 simply incised, the incisions being pointed. 



The specimen shown in fig. 1 is the best preserved, and 

 one of the largest. Its diameter measures 84 mm., with an um- 

 bilical width of 40 mm. The ribs number 43 in the last whorl, 



