10 THE MOLLUSC A OF MUSCATINE COUNTY. 



have seen from this State is 24 mm. long ; aperture, 16 mm. ; 

 and greatest width, 14 mm. Whirls, about C ; spire very 

 acute. This form has been called heterostropha (Say) by 

 many of our correspondents. 



P. heterostropha, SAY. Abundant. Length of shell, 19; of 

 aperture, 15 ; diam. of shell, 12 mm. Whirls, 5 ; first very 

 large ; epidermis very light horn color. 



P. ampullacea, GOULD. This may be a form of heterostropha; 

 but it has been called ampullacea^ and it corresponds to the 

 figure and description in Part II., "Land and Fresh- Water 

 Shells" (W. G. Binney). Length of shell, 19 ; of aperture, 

 13; diam., 10 mm. Whirls, 5, reddish horn color; shell 

 firm. 



P. virgata, GOULD. I discovered this beautiful little Physa in a 

 pond in South Muscatine, in the spring of 1877, along with 

 ampullacea and heterostropha. The pond became dry the 

 following year ; and it has not been found elsewhere in this 

 vicinity. Length of shell, 10 ; of aperture, 7.5 mm. 



PLANORBIS. 



P. trivolvis, SAY. Common. This species is protean. 

 P. bicarinatus, SAY. Common. Diam., 12 mm. 

 P. exacutus, SAY. Common. Diam., 6.6 mm. 

 P. deflectus, SAY. Somewhat rare. Might be mistaken for albus. 



Diam., 6 mm. 



P. albus, MUL. Common. Diam., 6 mm. 

 P. parvus, SAY. Common. Diam., 4 mm. 



SEGMENTINA. 



S, armigera, SAY. Hardly common. We have called this species 

 wheatleyi heretofore; but, on careful examination, it seems 

 to be armigera. Diam., 7 mm. 



ANCYLUS. 



A, diaphanus, HALDEMAN. Somewhat rare. This species was 

 identified for us as fuscus; but, on studying the figures and 

 description in "Land and Fresh-Water Shells," Part II. (W. 

 G. Binney), I am satisfied our Ancylus must be diaphanus, 



