288 "THE CHICAGO ACADEMY OF SCIENCES. 



114. Planorbis trivolvis Say, pi. xxxii, figs. 7, 8, 9, 10. 



Planorbis trt 'volvis SAY, Nich. Ency., pi. ii, fig. 2, 1817. 



Bulla fluviatilis SAY, Journ. Phil. Acad., Vol. II, p. 178, 1821 



Planorbis lentus GOULD, Invert, of Mass., p. 202, fig. 132, 1841. (Not of 

 Say.) 



Planorbis regularis LEA, Trans. Amer. Phil. Soc., Vol. IX, p. 6, 1841. 

 (Juvenile?) 



Planorbis megastoma DE KAY, N. Y. Moll., p. 61, pi. iv, figs. 60, 61, 1843. 



Physa planorbula DE KAY, N. Y. Moll., p. 76, pi. v, fig. 83, 1843 (juve- 

 nile). 



Planorbis trivolvis\&t.fallax HALDEMAN, Mon., p. 15, pi. iii, figs. 1-3, 

 1844. 



Planorbis macrostomus WHITEAVES, Can. Nat., Vol. VIII, p. 113, fig. 

 1853. (Variety.) 



Planorbis plexata INGERSOLL, Survey of the Terr, p, 402, 1874. 



Planorbis distortus W. W. CALKINS, MSS. 



Cochlea trium orbum LISTER, Conch., pi. cxl, fig. 46. 



Shell: Sinistral,* discoidal, flat, carinate above, subcari- 

 nate below; color brownish or chestnut horn; surface shining, 



FIG. 96. 



Radula of PLANORBIS TRIVOLVIS Say. (Original.) c, central tooth; 

 1, first lateral; 8, intermediate marginal; 14, seventh marginal. 



lines of growth oblique, numerous, raised, equidistant; apex 

 almost submerged in the coils of the whorls; whorls four, dis- 

 coidal, rounded, subcarinate below, carinate above; spire flat, 

 in the young perfectly flat, but in the adult sunk below the level 

 of the last whorl, always exhibiting all the volutions; sutures 

 rather deeply indented; periphery rounded; base of shell in- 

 dented, showing from two and a half to three volutions, which 



