1916.] NATURAL SCIENCES OF PHILADELPHIA. Ml. 



Table IV. 



Locality. Substratum. Striped Shells. 



Blue Hill Hay Chlorite schisl l.l 



Red granite 



Western Way ......Chlorite schisl 27 % 



Red granite 1 (avrratic oi Is collec- 



t ions from this region) 1 1.-1% 



Western Way Chlorite schist 27 ' , 



Nearest Granite Station Red granite 18.")', 



The distance apart of the stations introduces so many other factors 

 that with such meagre data no conclusions can be drawn. The 

 writer expects that the results are really negative. 



The relative proportions of the imbricated forms from different 

 localities are as follows : 



In the upper bays the water is much warmer than near the ocean. 

 This warmth is indicated at Blue Hill by bathhouses being located 

 along the beaches. Xone of the resorts farther down the bays have 

 any, the water being too cold for bathing in the bay in those places. 

 The upper bays are relatively shallow and there are muddy spots 

 found on the rocky beaches between the rocks. Five stations in this 

 region had imbricata ranging from 38% to 96%. 



In the middle bay region of Blue Hill Bay the water is deep and 

 the rocky shores are clean. Xo imbricata were found in the three 

 stations in this region. 



The western side of lower Blue Hill Bay is shallow, with many 

 islands and ledges. Among these islands there are many mud flat- 

 and the same conditions are found on the upper bay. Five station- 

 had imbricata ranging from 9% to 30%. 



Near the islands separating the lower bay from the ocean the 

 water is, in general, deep and the rocky shores clean. Five stations, 

 0-5^% imbricata. 



On the outer islands the surf, of necessity, keeps the rocks free 

 from sediment. Two stations, 17-57%. 



In Somes Sound environmental conditions similar to those in 

 Blue Hill Bay are found. The rocks are muddy in the harbors near 

 mud flats and clean where wave action is possible and the water i- 

 deep. If we except two stations at the Southwest Harbor steam- 

 boat wharf, where the ratio of imbricata was 19% and 19.2%, respe 

 ively, the average of thirty-five stations containing 7,119 individuals 



1 Of these eighteen collections, four had over _'. ' , striped, one had ■'•. 



