Baker — Notes on a Collection of Mollusks. 7 



spcc'miens have a low spire. Specimens from Alpena are 

 small, veri/ smooth and shining. 



This species is made to bear the sins of the whole Physa 

 family, many couchologists placing everything from gyrina 

 to ancillaria in it. It is, however, a very distinct species, 

 easily recognized by its smooth, glossf/ shell, oval aperture 

 and regular, pointed spire. It may also be known by the 

 absence of the various rest periods, the growth being com- 

 pleted in one year, while gyrina occupies t/u^ee years in com- 

 pleting its growth. It is not as common as most of the other 

 northern Physae. 



Physa ancillaria crassa Walker. 



(PI. I. Figs. 7, 8,9, 10). 



Long Lake; Thunder Bav Island. 



This very distinct variety seems to be the most abundant 

 Physa in the region under consideration, about 150 specimens 

 being in,the collection. It is easily known by its Ae^vy shell, 

 extremely short spire, shouldered whorls and the two or three 

 heavy, white, varicose bands which show through the shell. 

 Typical specimens measure as follows : 



Length 13.00; width 8.00; aperlurj length 10.00; width 4.50 mill. 

 " 13.00; " 800; " " 9.00; " 4.25 " 



Mr. Walker's description in the Nautilus XIV, p. 98, 

 1901, will readily distinguish this variety which seems to take 

 the place of typical ancillaria in this region. 



Another form occurs with variety crassa (figs. 9, 10), 

 which is referred to it by Mr. Walker, but which differs from 

 that form in several respects, apparently standing between 

 ancillaria and crassa and resembling in a measure, Physa 

 sayii Tappan. The spire is acute and somewhat elevated, the 

 whorls are gracefully rounded and there is no evidence of a 

 shoulder. The shell is thick and solid and the varicose ribs 

 of crassa are present. Specimens measure as follows : 



Length 14.00; width 8.00; aperture length 10.00; width 4.25 mill. 

 ♦< 12.75; " 8.50; '' " 9.00; " 4.00 «' 



" 16.00; " 9.50; «' " 12.00; " 5.00 " 



