So 



The following species were more or less common along the shores of Omori vil- 

 lage, but have not yet been found in the Mounds. 



Maetra, possibly sulcataria. 



Ca nee //aria Spengleriana Lischke. 



Soletellina o/iracea Jay. 



Liocardium sp. 



Pecfen sp. 



Nat tea janthostoma Deshayes. 



With the exception of the last species, these are all edible mollusks, and the 

 Maetra is one of the most common mollusks in the Tokio markets. Their ab 

 sence from the Deposits certainly indicates a change in the fauna. 



In this respect the absence of Halwtk and Pinna from the Mounds is certain- 

 ly of great interest, for it shows, either the lack of proper means for water trans- 

 port, or a disinclination on the part of the people to go far from their abiding 

 place in quest of food. 



On the opposite side of the Bay, and also south of Yokohama, the Ha/iotis 

 may be found, and large numbers of the shells are brought to Tokio for the 

 pearl they afford. No trace of the large species, Ila/iotis gigantea or of the small- 

 er species, Haliotis Grauer i, has as yet been met with in the Mounds. 



A race of fishermen accustomed to venture far in their boats would certainly 

 have left some trace of these species in their refuse piles. 



In conclusion it may be said that a pronounced change lias taken place in the 

 molluscah fauna of the Bay of Yedo since the Omori deposits were made. 

 The extinction of certain forms within comparatively recent times might be 

 accounted for in considering the upheaval of the water basin, aud the conse- 

 quent narrowing of the Bay aud shoaling of the waters, but the profound 

 changes which have taken place in the size and contour of certain species de- 

 mands time. 



There are but few units of time that can be used to measure the interval 

 required to effect such changes. One of two hundred and thirty years has 

 presented itself to me in the removal of a portion of the Suruga-dai canal 

 embankment. This canal was dug through Suruga-dai two hundred and thirty 

 years ago. The earth was piled up in immense embankments on each side of 

 the canal. 



Becently at Misaki Cho, near the Suido Bashi, a portion of this embankment 

 was removed in the construction of a new street. In the removal of this earth, 

 a deposit of shells was exposed presumably as old as the embankment, which 

 rested upon it. 



The deposit was composed of the following species. P/aeaanmnia sp, Ostrea 

 de»n/an>e//osa, Östren sp., Ci/therea merefri.-r, Cyelina C/iivensis, Maetra veneri- 



