4 ART. 6. — M. YOKOYAMA ON SOME 



The fossils found in Bed I are all new. But the resemblance 

 of Perna to Perna rugosa of the Dogger and the occurrence of 

 a costated Triyonia which has its greatest development in the 

 same formation and of the genus Cyrena which is abundant in 

 the Middle Jurassic plant-bearing series of other parts of Japan 

 tend to show that the bed is still Middle Jurassic, possibly be- 

 longing to its upper part. 



Beds IT. and III., although their j^ahieontological characters 

 are not yet known, must be considered as belonging also to the 

 Dogger, as they lie between I. and IV. 



From what has been said above, it is quite clear that the 

 strata are inverted. Bed VI. which Professor Jimbo considered 

 as uppermost being the lowest, and Bed I which was taken by 

 him as the lowest being uppermost. According to my opinion, 

 the so-called line of unconformability betwceJi III. and IV. may 

 possibly be a line of fault. 



DESCRIPTIONS OF THE SPECIES. 

 A. Fossils from Bed VI. 



1. SCHLOTHEIMIA JIMBOI xv. sp. 



PI. I, Fig. ('.. 



The I'orm which I designate under the above name is a 

 discoidal shell somewhat distorted 1)y pressure. Its diameter 

 measures about o4 nnn, while that of the umbilicus is about G 

 mm, so that the shell may be said to be tolerably widely um- 

 bilicated. The lateral sides of the whorls are only slightly convex 

 and ornamented with somewhat ilexuous ribs which number o8-40 



