214 Dr. H. Yabe — New Pleistocene Fauna from Tokyo. 



The fossil contents of the Narita Series are almost exclusively 

 confined to Mollusca and a species of Echinoderm, although naturally 

 other fossils, for example, Foraminifera, Corals, and Crustacea, are not 

 excluded, heing relatively so seldom met with that they may be 

 considered of no practical value for classification of the beds. Of the 

 Mollusca the great majority belong to the Lamellibranchia (or 

 Pelecypoda), which much exceed the Gasteropoda in number of 

 species as well as in quantity of individuals. The molluscan fauna 

 of the " Narita Series" is equal in number of species to that of 

 the shell-beds of Shinagawa and Oji ; but a striking feature of the 

 former is the exceeding preponderance of certain forms over others, the 

 most conspicuous species being Mactra sulcataria, Tapes philippinarum, 

 Tellina vennlosa, Solen hrmenstemi, Diplodonta pacifica, and Pecttmeulus 

 alholineatus ; Echinorachnius mirabilis belongs also to the same category, 

 and in some localities it is found almost alone and without the presence 

 of other fossils. 



Another characteristic feature of the fossiliferous bed in a typical 

 development is its contents of triturated shell-fragments in great 

 quantity, beside its mineral composition, so that the term shell-sand 

 seems really appropriate. The shell-remains vary in preservation and 

 are generally very water-worn ; the Pelecypoda are seldom found 

 with both valves associated. The formation of the fossiliferous bed 

 might have originated just in the same way as obtains at present 

 along an ocean coast exposed to the violent abrading action of mighty 

 waves. The shell-bearing sand of Oji and Shinagawa was formed 

 in a different way; the Pelecypoda are often found with both valves 

 connected and in the position which, they assumed during the living 

 state, and there are besides numerous vertical sand or clay-tubes n<>t 

 in the least distorted ; such conditions would tend to prove that 

 sedimentation took place in quite calm water. 



Stratigraphically the JSTarita Series, at least in its upper part, is 

 decidedly younger than the shell-beds of Shinagawa and Oji, but 

 whether its lower part is not synchronous with the latter is at present 

 questionable; the faunal difference seems in this case to depend more 

 upon the geographical separation and the difference of the physical 

 conditions of the places where the marine sediments were deposited 

 than on the slight difference of age. The question of the relative 

 geological age of these two faunas is only to be decided by means 

 of a boring at a proper place in the district of the Narita Series, 

 unless the typical Oji fauna is found beneath the shell-sand of the 

 Narita Series. 



The sandy gravel bed between the loam and the brown and blue 

 clay of Tabata is considered by me as a special development of the 

 Narita Series, or at least of its upper part; the sandy gravel bed 

 passes on one side into an immense accumulation of gravels of various 

 sizes, and on the other side to fine sand with cross-bedding ; fossils 

 are very seldom found in it, but I can safely conclude from material 

 at my disposal l that the formation of the deposit is either marine or 

 coastal, at all events so far as the deposit in Tokyo is concerned. 



1 Professor B. Koto and I have collected in the sandy gravel bed of Shibuya 

 (in Tokyo) Ncptanca dcspecta and Cancellaria nodulifera. 



