168 MOLLUSCA. 



tude 9.5mm., width 6.5mm., aperture length 6.75mm., aperture width 

 3mm. The deformity of the other specimen has apparently been 

 caused by an injury near the beginning of the last whorl, which is 

 greatly enlarged. The shell measures: altitude 12.25mm., width 

 9.25mm., aperture length 9.5mm., aperture width 5mm. 



79. Physa ancillaria, var. magnalacustris Walker. — This variety 

 was collected in considerable numbers on the limestone rock bottom 

 off the north shores of North and Stony Islands (2), and from rock 

 pools along 'the shore of the former (3). A thin form was also found 

 on the rocks of a wharf off the north shore of Sand Point. An ex- 

 ample of the former measures: altitude 14.25mm., width 10mm., 

 aperture length 11mm., aperture width 6.25mm.; of the latter: alti- 

 tude 15mm., width 11mm., length of aperture 12.25mm., aperture 

 width 7mm. 



80. Physa sayii Tappan. — A single specimen of this species was 

 obtained from Turtle Bay (8), from the under-side of a piece of drift- 

 wood. It measures: altitude 17mm., width 9.75mm., aperture length 

 13mm., aperture width 6.25mm. 



81. Physa heterostropha (Say). — ^This species was fairly abundant 

 and quite widely distributed in the region studied. It was found as 

 follows: in the sedge marshes (7) and on lily-pads in Turtle Bay (8), 

 at Sand Point ; on rocks off the north shore of North Island (2) ; among 

 algae along the shores of the Pigeon River (21) and on the under-side 

 of lily-pads and driftwood and among Potamogeton in the ox-bow 

 pond off the river (22); and on the under-side of lily-pads in the 

 mucky-bottomed portions of Rush Lake (11). The specimens ob- 

 tained from North Island are very light-colored, some of them being 

 pure white. All of the specimens are quite small: one of the largest 

 measures: altitude 10.25mm., width 6.25mm., aperture length 7.75 

 mm., aperture width 3.25mm. 



82. Physa gyrina Say. — ^This shell was more abundant locally than 

 the preceding and was almost as widely distributed. It was found 

 on driftwood in the sedge marshes (7) and on driftwood and among 

 grass in Turtle Bay (8), at Sand Point; on the under-side of hly-pads 

 in the dead waters several miles up the Pigeon River (24); and in 

 temporary and perennial swamps (18, 19) and in a county drain (17) 

 at Rush Lake. The shells are mostly small; the largest one measures: 

 altitude 16.5mm., width 10.75mm., aperture length 12.5mm., aperture 

 width 6.5mm. 



83. Physa gyrina, var. hildrethiana (Lea). — A few' specimens of this 

 variety were obtained from a temporary swamp (18) near Rush Lake. 

 The largest one measures: altitude 14mm., width 7.5mm., aperture 

 length 10.5mm., aperture width 4.75mm.; it is considerably malleated. 



