JURASSIC AMMONITES FROM ECHIZEN & NAGATO. 6 



forms; viz. Perisphinctes Hatsushimai to Perisphinctes promiscuus 

 Bukow.j Perisphinctes kaizarawus to Perisphinctes triplex Quenst, 

 and polygyratus Rein., Perisphinctes Kochibei to Perisphinctes 

 subcolubrinus Waag., and Perisphinctes sp. to Peri. *j >ki notes oc- 

 cullefurcatus Waag. The only other Ammonite beside Peri- 

 sphinctes is a new form of Oppelia which exhibits a distant 

 relationship to OppeUa nob His Neum. of the Tithonian. There- 

 fore it is hardly to be doubted that we have here a bed which 

 must be ascribed to the Malm. This assertion is also strengthened 

 by the preponderance of Perisphinctes which has its greatest 

 development in the same formation. To what part of the Malm 

 this Ammonite-bed belongs is at present difficult to say, but 

 probability points to its lower part or Oxford. 



The determination of the Echizen Ammonites as those of 

 the Malm leads to the important conclusion that the plant- 

 bearing series developed in that part of Japan is not, as formerly 

 believed, entirely Middle Jurassic, but that a part of it represents 

 also the upper portion of the same formation. 



DESCRIPTION OF THE SPECIES. 



1. PERISPHINCTES (PROCERITES) MATSUSHIMAI M. 



PI. I. Fig. 1. 



The shell is compressed, discoidal, widely umbilicated, con- 

 sisting of about G whorls which are nearly ! involute. The 

 whorls are also laterally compressed, being only slightly convex. 

 They are furnished with many rigid elevated ribs separated by 

 smooth intervals of a much greater breadth. These ribs are 



