THE NATURAL HISTORY SURVEY. 311 



very beautiful and precisely as described for gyrina. This spe- 

 cies has been found in all the regions, at Joliet, Maywood, 

 Lake Calumet and Lake Michigan near Oak street. Sayii is 

 apparently closely related to P. ampullacea Gould, a Pacific 

 Coast species. 



Sayii appears like gyrina and some other species, to be 

 dimorphic, having a short- and a long-spiral form. Were it 

 not for the closely connecting individuals, the short-spiral form 

 would be worthy of varietal distinction; see plate xxxii, fig. 13, 

 and plate xxxiv, fig. 7, where the short-spired form is figured. 

 Sayii is an annuan. 



127. Physa gyrina Say, pi. xxxiv, fig. 4. 



Physa gyrina SAY, Journ. Acad. Nat. Sci., Phi)., Vol. II, p. 171, 1821. 

 Physa striata MENKE, Syn. Meth., ed.2, p. 32, 1830. 

 Physa hildrethiana LEA, Proc. Amer. Phil. Soc., Vol. II, p. 32, 1830. 

 Physa cylindrica NEWCOMB in DE KAY, N. Y. Moll., p. 77, pi. v, fig. 82, 



1843. 



Physa plicata DE KAY, 1. c., p. 78, pi. v, fig. 85, 1843. 

 Physa hawnii LEA, Proc. Phil. Acad., p. 115, 1864. 

 Physa par-va LEA, 1. c., p. 115, 1864. 



FIG. 109. 

 Surface sculpture of PHYSA GYRINA Say. (Original.) 



Shell: Elongated, generally polished, whorls five to six; 

 spire always very long, as compared with the last two species, 

 acute, the whorls in some cases almost flat, and at best but 

 slightly convex; color varying between light greenish horn 

 and brick red; sculpture consisting of well-marked growth 

 lines, crossed by numerous fine impressed spiral lines, giving 

 the shell a wrinkled appearance (Fig. 109); these lines appear 

 at first to be raised, but when viewed through the microscope 

 are seen to be impressed between two wrinkled ridges, as 

 shown in the cut; sutures scarcely- impressed, bordered by 

 a porcelain-white line which is rarely edged with chestnut; 

 aperture rather long, long-oval in form, much narrowed at the 



