26 SIXTEENTH REPORT. 



and large numbers of these species were landlocked, and subsequently many 

 of them killed, during the summer of 1911. Physa ancillaria parkeri must 

 have bred here also, as the juvenile specimens were found, in considerable 

 numbers, during the summers of 1911, and 1913, and to some extent in 

 1912. Small specimens approaching Physa ancillaria magnalacusiris were 

 also obtained. 



II. SAND SPIT TYPES. 



On the other hand, the sand spit pools of Douglas Lake, like the barrier 

 beach pools of Saginaw Bay, were major features and often predicated a 

 long life history. Four lagoons and pools, in different stages of completion, 

 were studied; these were, in order of their apparent age: the Pine Point 

 Lagoon, the Hook Point Lagoon, the Swamp Point Lagoon, and the Sedge 

 Point Pool. The situations of these four were more or less similar, in that 

 they all were produced along the north-east side of the lake, the first two 

 and the last along the shore north of North Fish Tail Bay, the last on its 

 south shore. They apparently were produced by the currents that were 

 diverted along the shore of the lake to the east of the triangluar bar already 

 mentioned. 



a. Description of Different Examples. 



1. The Pine Point Lagoon. (Map 2, b; map 7). During the summer of 

 1912, a spit was initiated to the south-east of Pine Point by a heavy storm 

 from the west and south-west; in the summer of 1913, this had developed 

 far enough to partially enclose a small lagoon. This was choked with Scir- 

 pus americanus, and also contained a few scattered potamogetons, Eleo- 

 charis, bunches of Chara, etc. The bottom was at first of sandy marl, 

 similar to the bottom of the shelf in that portion, but soon accumulated 

 considerable quantities of debris, muck, etc. 



Clams. 



Anodonta grandis footiana (Lea). Infrequent; a few stray specimens were 

 noticed. 



Primary species. 



Campeloma decisum (Say). Abundant. 



Planorhis bicarinatus, var. approaching portagensis Baker, shelf form. 



Abundant. 



Physa ancillaria parkeri (Currier). Common, during breeding period. 



Lymnaea emarginata angulata (Sowerby). Frequent; during breeding 

 period. 



Planorhis campanulatus smithii Baker. Infrequent. 



Lymnaea stagnalis perampla Walker. Very infrequent; during breeding 

 periods. 



Secondary species. 



Planorohis hicarinatus, var. juvenile. Abundant. 



Physa ancillaria parkeri (Currier); juvenile. Very common. 



Planorhis parvus Say. Frequent. 



Lymnaea emarginata angulata (Sowerby); juvenile. Frequent. 



Amnicola limosa (Say). Frequent. 



Valvata tricarinata (Saj^, and var. confusa Walker. Infrequent. 



2. The Hook Point Lagoon. (Map 2, c; map 8). Inside the inner curve 

 of the sand spit, at the end of Hook Point, was a marshy lagoon in which the 

 water was quite shallow, reaching a depth of 30 cm. The shelf adjacent 



