and these shells are called sinistral or left-handed shells. Some shells, 

 as a variety of the apple snail, Campeloma decisum, may be either 

 dextral or sinistral, but only a few species of snails are both right and 

 left handed. 



The animal of the Physa seemed similar to that of the orb shell, 

 the tentacles being long and slender, and George asked if there was 

 any difference. The Professor suggested that we examine a specimen 

 carefully. This we did, and found that it differed from all the other 

 fresh-water snails in having many little finger-like projections on the 



edge of that part of the mantle covering the 

 columella. These were arranged in two series 

 of rows, one near the lower part of the columella 



^ Animal of Physa. (Bin- and Qne near the point Q f j imcture of the Ollter 



lip with the body whorl. The whole animal 



was yellowish gray or blackish in color, flecked with yellowish white, 

 the spots being plainly seen through the transparent shell. 



Professor Parker then told us that Physa was one of the hardiest 

 of snails, and that he had frequently seen it in winter gliding over the 

 bottom of a pond or creek when the surface was covered with ice. 

 The shells, he said, were very variable, scarcely two specimens being 

 exactly alike. 



A short distance from the shore of the creek were a number of dead 

 clam shells, and George fished up several of them with the wire net. 



One of these shells had several little snails upon it 

 which were quite new to us. These snails were 

 flat and limpet-shaped, and about a quarter of an 

 inch in length. The animals looked like Limncea, 

 with their flat, triangular tentacles and broad foot. 



R i v er yl lhnp r e V t U wSh The Prof essor said that these curious little f resk-water 

 animal extended, limpets, Anci/lus, were very common on both the out- 

 side and inside of clam shells, and on stones, sticks, 

 and other submerged objects. 



Having exhausted this part of the creek as a collecting locality, a 

 shady spot was selected in which to eat lunch, and never was feast 

 more enjoyed than was that simple lunch, the appetites being whetted 

 to the keenest edge by the fresh air and vigorous exercise. 



After lunch, our party walked across several fields, passed through a 

 patch of woods, and crossed a stretch of swamp, where Howard fell into 

 a hole, thereby scaring several water fowl. Finally we reached the 

 shore of a large lake, where Professor Parker said another type of mol- 

 lusk was abundant. 



14 



