416 



THE CHICAGO ACADEMY OF SCIENCES. 



from Maine, Michigan, Wisconsin and Minnesota has demonstrated 

 that the species is divisible into a number of fairly well-marked races. 

 In all of these races there are some individuals which approach typical 

 emarginata in general form showing that all have sprung from the 

 same stock. Each race, however, expresses a certain facies which 

 easily separates it from the typical form and from the other races. The 

 relationship of these races may be expressed as follows: 



emarginata 



mighelsi 



angulata 



wisconsmensis 



ontariensis 



canadensis 



Wisconsincnsis is somewhat related to mighelsi and angulata, but 

 on the whole seems to present characters which place it as an inde- 

 pendent branch of emarginata. 



The Maine emarginata varies toward mighelsi, some individuals 

 being of such a transition character that they cannot be definitely 

 placed in either form (as figures 10-11 on plate XLIII). As a rule, 

 however, the rounded aperture and more elevated spire will separate 

 the two forms. The figures on plate XLIII well illustrate this varia- 

 tion. Emarginata from Michigan and New York are more uniform 

 and less difficult to determine. Specimens from Western Ontario 

 (especially Rainy Lake) vary towards mighelsi. 



Galba emarginata mighelsi (W. G. Binney). Plate XLIII, 

 figures 13-21 ; plate XLI, figure 25. 



Limnaa ampla MIGHELS, Bost. Journ. Nat. Hist., IV, p. 337, 1843; Best. 

 Journ. Nat. Hist., IV, p. 347, pi. 16, fig. 1 a to 1 c, April, 1843 (not of Hartmann 

 1842) ; Proc. Bost. Soc. N. H., 1, p. 129, 1843. STIMPSON, Sh. N. Eng., p. 52, 1851. 

 WHITEAVES, Can. Nat. & Geol., VIII, pp. 102, 112, fig. 11, 1863. BINNEY, Check 

 List, p. 12, 1860 ; Land & F. W. Sh. N. A., II, p. 30, fig. 34, 1865. MORSE, Amer. 



