102 MARINE AND FISHERIES 



5 GEORGE v., A. 1915 

 Family physidae. 



Represented by six species belonging to two genera, Physa and Ancylus. 



Genus Physa. 



Of this genus five species were obtained. Four of these are large and dark- 

 colored, have short spires, thin shells and indistinct sutures and occur throughout 

 a wide range of habitat. The fifth is small, light colored, with white varical thick- 

 enings of the whorls, has a more elongate spire and is found only on semi-exposed 

 rocks. Although the two groups are quite distinct, the species within the first 

 group are not so clearly differentiated. The characters upon which the species of 

 this genus are based are exceedingly variable and the extremes of variation grade 

 into one another so smoothly that an attempt to verify the present classification 

 by breeding experiments and anatomical investigation seems desirable. The writer 

 intends to undertake the task in the near future. In the meantime the distinctions 

 here used will be those of the literature of the genus. 



Physa heterostropha, Say, occurs usually in protected situations in weedy bays 

 or quiet rocky channels, rare. Surface smooth and shiny, without sculpture, the 

 spire elevated and the sutures distinct. Food, diatoms, desmids and other algse. 



Physa ancillaria, Say, very abundant, almost everywhere in sheltered bays 

 and along partially exposed shores. In the spring it may be seen collecting in vast 

 numbers to the breeding-grounds in rocky channels and in the bays of rocky islands. 

 Within a few days after copulation the eggs are laid in elongated capsules. A 

 single individual may lay as many as five capsules containing in all 150-300 eggs. 

 Spire short, sutures not so distinct as in P. heterostropha. Shell more robust than 

 in that species. Surface smooth and shining, sculptured. Varies much in surface 

 sculpture, height of spire, size and shape of aperture and number of digitations on 

 mantle. Such malformations as forked tentacles and lobes arising from upper sur- 

 faces of foot were found. Food consists of diatoms, desmids and other green algae. 

 A number were found in whitefish stomachs. (PI. XI, Fig. 19). 



A variety, magnalacustris, Walker, with white lines on body whorl also occurs. 



The variety vinosa occurs in sheltered bays and on partially exposed shores. 

 Shell robust, spire short but sharp; whorls rounded and suture distinct. 



Physa gyrina, Say. Not very abundant, found in sheltered bays. Differs 

 from P. ancillaria in larger size, more elevated spire, more slender form and coarser 

 surface sculpture. 



Physa integer niagarensis, Lea; found on somewhat exposed rocky shores, 

 much smaller than any of previous forms, shell much like a small reversed L. 

 emarginata canadensis. Shell light horn with many white bands transverse to 

 whorls. Shell heavy, spire elevated, apex sharp, sutures distinct and whorls 

 rounded. Identified by Dr. Pilsbry. 



