136 PROCEEDINGS OF THE NATIONAL MUSEUM.. vol.xxii. 



LIMNiEA DESIDIOSA Say. 



Eagle Lake; two living examples (Oat. ^o. 123895, U.S.N.M.). 



LIMN^A EMARGINATA Say. 



Eagle Lake ; abundant. Of the total number of shells from this lake, 

 nine-tenths belong to this species and its varieties, numbering, perfect 

 and imperfect being counted, probably four hundred examples. 



A. Normal form (Oat. No. 123887, U.S.N.M.); smooth; spire modera- 

 tely elevated; rather solid and ventricose; columellar fold or twist, 

 rather strong. 



B. Spire short (Oat. No. 123888, U.S.N.M.); rather thin and ventri- 

 cose, ranging from young to adult. 



0. Body lohorl shouldered above (Oat. No. 123889, U.S.N.M); spire 

 short to elevated ; surface smooth to malleated ; solid. 



D. Deeply sutured; spire rather high (Oat. No. 123890, TJ.S.N.M.); 

 surface smooth; some individuals marked by strong incremental lines; 

 others inconspicuously lirate; young to adult. 



E. Malleated; obtusely Urate (Oat. No. 123891, U.S.N.M); in some 

 examples partially obtusely lirate; others showing sharply developed 

 growth lines; spire moderate; shell rather solid; aperture effuse; 

 numerous examples. 



F. Patulous; aperture more or less reflected (Oat. No. 123892, U.S.N.M) ; 

 surface smooth or malleated; obtusely lirate in some instances; spire 

 moderate; several examples. 



G. Distorted, bulging (Oat. No, 123893, U.S.N.M); shells globose or 

 elongated; solid; smooth or malleated ; suture deep; aperture in some 

 examples effuse; numerous specimens. 



H. Immature (Oat. No. 123894, U.S.N.M.); this number and tube 

 includes juvenile examples of many of the foregoing, and other varietal 

 facies. 



PLANORBIS TRIVOLVIS Say. 



Heron Lake; abundant (Oat. No. 104462, U.S.N.M.). A dwarfed and 

 apparently arrested form of this widely distributed species was obtained 

 in great numbers by Mr. Bailey. The largest individual measured, 

 maximum, only 12.50 mm., while the average of numerous examples is 

 not over 9 mm., maximum. There are two varietal forms, which point 

 to hybridization, suggesting campanulatus in one direction and bicari- 

 7iatus in the other. Among 143 perfect individuals, exhibit the abrupt 

 varicose character of aperture so conspicuous in campanulatus, and there 

 are many examples that lean toward blear ina-tus, with a pretty sharp 

 angle on the upper and an obtuse keel on the under side of the whorls. 

 These are registered in the United States National Museum, as follows: 



P. trivolvis var. A (Oat. No. 104463, U.S.N.M.). 



P. trivolvis var. B (Oat. No. 104464, U.S.N.M.). 



