260 THE CHICAGO ACADEMY OF SCIENCES. 



A recent study of numerous species of this genus has 

 convinced the writer that some classification other than the 

 one in use must be found. The present grouping by shell 

 characters is totally unsatisfactory on account of the extreme 

 variability of the individuals. For example, different forms 

 of L. emarginata Say v&r.mighelsi Binney, recently examined, 

 can be placed in all of the so-called subgenera usually recog- 

 nized (Radix, Bulimnea, Limnophysa, etc.), and in fact the typ- 

 ical emarginata is typical of Limnophysa, and the variety 

 mighelsi of Radix; all of the intermediate forms occur and 

 absolutely connect the extremes. In view of this fact the 

 writer has discarded all subgenera, using simply the generic 

 term Limnaea. Some divisions of value will undoubtedly be 

 found when all of the species are examined anatomically for 

 the genitalia, radula, etc. There is abundant work in this line 

 for a naturalist having the time and material at his command. 



104. Limmua columella Say, pi. xxx, fig. 26. 



Limncza columella SAY. Journ. Phil. Acad., Vol. I, p. 14, 1817. 



Limncea navicula VALENCIENNES, Rec'd. Obs., Vol. II, p. 251, 1833. 



Limncea chalybea GOULD, Am. Journ. Sci., ed. 1, Vol.XXXVIII, p. 196, 

 1840. (Variety.) 



Limncea acuminata ADAMS, 1. c., Vol. XXXIX, p. 374, 1840. 



Limncea strigosa LEA, Proc. Amer. Phil. Soc., Vol. II, p. 33, 1841. 



Limncea coarctata LEA, 1. c., p. 33, 1841. 



Limncea casta LEA, 1. c., p. 33, 1841 . (Variety.) 



Succinea pellucida LEA, Proc. Phil. Acad., p. 109, 1864. 



Limncea columellaris ADAMS, Amer. Journ. Sci., ser. 1, Vol. XXXVI, 

 p. 392, absq. descr. 



Limncea succiniformis ADAMS, MS., teste Haldeman. 

 Shell: Ovate, somewhat pointed, thin, fragile, transpar- 

 ent; color light greenish or yellowish horn; surface shining, 

 covered with rather coarse growth lines, and encircled by im- 

 pressed spiral lines; whorls four, rounded, rapidly enlarging, 

 the last one three times the size of the rest of the shell; spires 

 sharply conic, rather short; apex small, very dark brown; su- 

 tures impressed; aperture ovate, dilated, expanded at the lower 

 part; the aperture varies from long and narrow to wide and 

 somewhat expanded; peristome thin, acute; columella narrow, 

 twisted; terminations of peristome connected by a thin callus; 

 umbilicus generally closed but sometimes very narrowly per- 

 forate where the callus is not fully developed; the columella 

 is so narrow that a view may be taken from the base nearly to 

 the apex, as in Succinea retusa. 



