25 



"With these facts before me, I was impelled to examine tlie various species ■ t 

 shells found in the Omori Mounds, in comparison with similar species now 

 living along the immediate shores of the Bay. The followiugs descriptions and 

 measurements will show that changes more or less great have taken place since 

 the ancestors of those now living along the shore formed the food of the savages 

 who made the deposits. 



As a preparation for these comparisons, a number of visits were made to the 

 shores of Omori village, in which I was accompanied by a class of special 

 students and others who had collected with me in Yezo. 



A. most searching exploration was made along the coast for a considerable 

 distance, and many 'specimens of every species bearing upon the subject were 

 obtained. A sjiecial search was made for those forms common in the Mounds. 

 A similar number of visits was made to the Mounds, accompanied by the same 

 corps of assistants, with directions to collect every species found there. In this 

 way an immense amount of material was brought together, and from this mate- 

 rial only mature and perfect specimens were selected for comparison. Besides 

 this material, I had a large number of species collected at Yenoshima, year 

 before last, as well as a large amount of material collected by the University 

 Expedition at Otaru and Hakodate, in Yezo, Sendai Bay, and on the west coast 

 at Funagawa, and Niigata. Use was also made of valuable collections made at 

 Kishiu this winter by Prof. Yatabe and Mr. Sasaki. All of these collections 

 were of use in showing the degree of variation between Northern and Southern 

 forms of the same species. Collections of the edible mollusks in the Tokio mar- 

 kets, and at Shinagawa, were also considered in these comparisons. Measure- 

 ments were made in millimeters, and the tables of figures were submitted to Prof. 

 T. C. Meudeuhall, of the Tokio Daigaku, who kindly offered to compute the 

 averages and proportions for me. 



Every precaution has been taken to insure accuracj 7 ', and the results will 

 certainly be of interest to those who recognize a change in species, coincident 

 with change in time, and environment. 



Area xubcrenata Lischke. 



Specimens of this species were not uncommon in the Mounds, and were also 

 found scattered along the shores of the Bay. Lischke gives the number of ribs as 

 from 3.1 to 33. Twelve recent specimens from the shores of Omori averaged 33V,, 

 ribs, while 15 specimens from the Mounds averaged 30V 2 ribs. The hinge, or 

 umbonal area in the recent specimens, — measuring the area of one valve trans- 

 versely, gave an average of 5. 7 mm., while in the mound specimens the same 

 area averaged 5.9 mm. 



