446 THE CHICAGO ACADEMY OF SCIENCES. 



SOUTH DAKOTA: Grindstone Creek, Stanley Co. (Binney; Hay den). 

 WASHINGTON: Spokane, Spokane Co. (Olney). 

 WYOMING: Laramie, Albany Co. (Smith. Inst.). 



BRITISH AMERICA. 



ONTARIO: Lake of the Woods, Rainy River District (Dawson; Kennicott) ; 

 north shore, Lake Superior, Thunder Bay District (Ferriss). 



GEOLOGICAL DISTRIBUTION : Unknown. 



ECOLOGY : "It occurs here in great abundance chiefly in pools and 

 along the sides of the stream where it may be found clinging tightly to 

 the bare sandstone rocks and often in current so swift as to carry it 

 rapidly down stream when its hold is disturbed." (Ruthven, Mich. 

 Acad. Sci. VI, p. 189 ; Union River, Ontonagon Co., Mich.) 



"The Lower Beach is that portion of the shore .exposed to the 

 action of the waves during the summer months. At the point studied, 

 Station I, owing to the dip of the strata, the water deepens rapidly off 

 shore, and the breaker line is brought near to the beach, the lower part 

 of which is thus exposed to the full force of the waves. Exposed as it 

 is alternately to the pounding of the waves and dessication in the 

 sun the conditions are so severe that very little life can exist. The 

 only form that is found here is the snail Limnaa decollate, (^apicina) 

 that occurs occasionally behind projecting outcrops, where it is to some 

 extent protected from the direct force of the waves. This snail seems 

 to be adapted to habitats of this nature, for it was found elsewhere 

 only in rapid water in the larger rivers." (Adams). 



"Abundant on some parts of the shores of the Lake of the Woods, 

 generally among rocks and boulders on an exposed coast, creeping over 

 the stones even in the wash of the waves, with the habitat of a Lit- 

 torina." (Dawson, Lake of the Woods specimen). 



REMARKS: Apicina may be known by its globose, tumid shell, 

 rather short spire and conspicuous columellar plait. It somewhat re- 

 sembles both catascopium (short spired forms) and woodruffi but dif- 

 fers in having a more globose shell and a rounder aperture, and gen- 

 erally a broader and shorter spire. The shells agree well in the tumid- 

 ity of the whorls, but the spire varies from broadly acutely-conic to 

 tumidly depressed, and also varies one-half to nearly equal the length 

 of the aperture. The columellar plait is almost always very prominent. It 

 has been confounded with decollata, but that species is of a rhom- 

 boid shape, the spire is more regularly acute, the aperture is more 

 ovate, the last whorl is disproportionately swollen at the periphery 

 and the inner lip is more tightly appressed to the umbilical region leav- 

 ing no sign of a chink. 



