31 



Area subcrenata, Cycüna Chinensis, Cytherea meretrix, Mactra vemrifornm and 

 Doainia Troschrii. Area granosa is much larger than any dimension given by 

 Lischke. 



Among the few gasteropoda which occur insufficient numbers for comparison, 

 the differences in proportions between the Mound specimens and the recent ones 

 are quite as conspicuous. 



Eburna Japonica Lisclike. Plate xvni. Fig. 9. 



This is a very common shell in the deposits, and is also found scattered along 

 the shores. It is very common further south in the Bay. 



The differences between the ancient and recent shells are easily recognized 

 without the aid of measurements. 



The recent shell, though larger than the ancient one, is not so broad compared 

 to its length, as in the ancient form. While both have the same average 

 breadth, the recent form is nearly six millimeters longer. This gives the recent 

 shell a more acute spire, while the ancient shell appears more robust. 



A large number of recent and ancient specimens were brought together, and 

 from these, the perfect and mature ones, for the purposes of measurement were 

 selected. 



The angle of the spire was measured in fifty specimens of the Mound and 

 fifty specimens of the recent, and the difference is shown in the following dia- 

 gram. 



Diagram showing angle of spire of Recent, 

 and Mound shell, Eburna Japonica* 



M 



The mean angle for the recent was 57 "45' , and for the Mound, was 6t°4o', 



