MICHIGAN ACADEMY OF SCIENCE. 25 



Lymnaea emarginata angulata (Sowerby). Bred in abundance, in similar 

 situations to the habitat of the juvenile specimens in group 2; came up in 

 latter part of July, slightly later than the preceding species. 



Physa anciUaria parkeri (Currier). Appeared common; in water from 10 

 to 35 cm. in depth, especially in places where there was a firm, marly crust. 

 Most numerous at about 20 cm. Apparently came up in the early part of 

 June. 



Planorhis hicarinatus percarinatus Walker. Frequent; in similar places and 

 at a similar time to the other variety of P. hicarinatus. 



Lymnaea sfagnalis perampla Walker. Frequent; bred in mucky-bottomed 

 and weedy situations. Found in great abundance near the middle of July 

 in the mouth of Bessey Creek in the summer of 1911. 



Planorhis campanulatus smithii Baker. Quite infrequent; bred mainly 

 along mucky-bottomed shores with the shelf form. The time was difficult 

 to determine as the deep littoral immigrants are difficult to distinguish from 

 the form which inhabited the shelf; apparently it was nearly coincident 

 with that of the varieties of P. hicarinatus. This variety was less com- 

 pletely a deep littoral form than were the others; the shelf form was not so 

 noticeably increased in numbers during the immigration. 



5. Shells of the vegetation zones. As has already been mentioned, there 

 were considerable areas at the edge of the shelf, especially along the mucky 

 shores, which were taken up by various aquatic plants. These zones only 

 occurred in the protected places. 



Primary species. 



Lymnaea stagnalis perainpla Walker, young shells. Quite infrequent. 



Secondary species. 



Amnicola liniosa (Say). Very abundant. 



Valvata tricarinata (Say), and var. confusa Walker. Quite common. 



Planorhis parvus Say. Quite common. 



Ancylus parallelus Haldeman. Frequent; especially on lily pads. 



Planorhis deflectus Say. Quite rare. 



B. MOLLUSCS OF LAKE LAGOONS AND POOLS. 



I. BARRIER BEACH TYPES. 



a. Barrier Beach Pools on South Point. (Map 2, a; maps 3, 4, 5, and 6.) 

 The barrier beach pools of Douglas Lake, as has already been mentioned, 

 were so small that their depth was less than the annual range of the surface 

 level of the lake itself, and so they were built and destroyed each year. On 

 this account, the shells of these pools were simply landlocked forms from 

 the lake itself, and showed no ecological succession of pool forms. 



These pools were mainly formed on South Point, on the northeast side of 

 the lake about midway between North and South Fish Tail Bays. They 

 were situated in a place that would have been open to the action of the strong- 

 est waves, except for the presence of a large triangular bar of peculiar forma- 

 tion (map 2,0), which caused the water to be not much more than a meter 

 deep for nearly a mile off shore. For these reasons, there were apparently 

 almost no shelf forms except the clams and Campeloma decisum. These la- 

 goons and pools were, however, favorite breeding places for Lymnaea emarginata 

 angulata, Planorhis hicarinatus portagensis and P. hicarinatus percarinatus, 



