138 MOLLUSCA. 



Lymnaea palustris, Apleza hypnorum. Sphaerium occidentale, and 

 Musculium truncatum were the t\'pical shells of the annual swamp habi- 

 tat in this region. All of these were found in large numbers at all of the 

 places where this habitat was studied, with the exception of Musculium 

 truncatum which was not found on North and Stony Islands where these 

 conditions were but poorly represented. In addition, there were found 

 in lesser numbers: at Sand Point, Lymnaea palustris zebra, L. p. michi- 

 ganensis, a slender, little-malleated form of L. palustris, Planorhis par- 

 ■ vus, p. umbilicatellus , Physa elliptica, and a small form of Musculium 

 partumeium.; on Stony Island, Segmentina armigera; near Rush Lake, 

 Planorhis parvus whlkeri, P. umbilicatellus, Physa gyrina, P. g. hildreth- 

 iana, Lymnaea palustris michiganensis, Segmentina crassilahris, a small 

 form of Musculium partumeium, and some shells of Lymnaea which 

 were too young to be indentified. 



19. Perennial sivamps. On Sand Point, Stony Island, and around 

 Rush Lake there are a few shallow ponds and marshes which do not dry 

 up in the summer, or, at least, have not for some time. Of course this 

 depends upon the dryness of the season, but the ones studied were those 

 that did not dry up during the summer of 1908, which was one of ex- 

 treme drouth thruout this part of Michigan. (PI. VIII b.) 



These habitats, then, are distinguished from the annual swamps by 

 their greater permanency. They intergrade into the latter, however, 

 and are probably converted into them thru filling-in by vegetation, etc. 

 They often have an aquatic vegetation of Riccia, duck-weeds, horn- 

 worts, etc., while around the edges are found the semi-aquatic bulrush 

 (Scirpus validus), Scirpus americanus, Equisetum ftuviatile, and other 

 sedges and rushes, the Equisetum being especially abundant in the sandy 

 regions. 



Planorhis trivolvis and Musculiwn securis appeared to be the typical 

 shells of this habitat: they were found in abundance at Sand Point, on 

 Stony Island and near Rush Lake. There were also collected, but in 

 lesser numbers: at Sand Point, Aplexa hypnorum, Segmentina armigera, 

 a form of S. crassilahris, Planorhis exacuous, Succinea retusa, Amnicola 

 walkeri, Physa elliptica, Musculium truncatum, Sphaerium occidentale, 

 a small form of Lymnaea ohrussa, an elongate form of L. reflexa, and L. 

 pcdustris michiganensis; on Stony Island, Musculium ryckhaltii, Plan- 

 orhis deflectus, P. hirsutus, P. nautileus, Lymnaea reflexa, and an elongate 

 form of the last shell; near Rush Lake, Aplexa hypnorum, Segmentina 

 armigera, Sphaerium occidentale, Lymnaea palustris, a form of Planor- 

 his parvus, and Physa gyrina. 



20. Sivamp in old stone quarry. About a half of a mile west of Little 

 Oak Point, there is an old stone quarry, Babbitt's Stone Quarry, which 

 is partially filled with Avater. Cat-tails and alders have grown up in 



