MICHIGAN ACADEMY OF SCIENCE. 
211 
sand which would make it very difficult for these species to live and feed 
in shallow water. These varieties appear to be purely the effect of the 
environment on the parent species as in the outlet of Douglas Lake into 
Maple river there were found adult Physa ancillaria parkeri (Currier) 
that had apparently migrated in to breed, juvenile specimens of the 
same species that could not be distinguished from those in the very 
shallow water on the shoals of the lake itself, and larger shells, con- 
nected with the juvenile ones by those of intermediate size, which were 
even narrower than typical Pliysa ancillaria Say!! One of these latter 
measured : altitude* 12 nun., diameter 6.1 mm., length of aperture 8.8 
mm., while a young specimen of the form parkeri (Currier) from the 
lake measured : 12.3 mm., 9.2 mm., 10.5 mm. I think it probable that 
this narrow form had been produced from the deep water form by the 
action of the conditions of the creek during a single generation. Similar 
but not so striking relations seemed to hold for Lymnaea stagnalis 
perampla Walker and L. stagnalis appressa (Say), the typical river 
form in this region ; Planorbis bicarinatus portagensis Baker and ty- 
pical P. bicarinatus Say; and perhaps also Lymnaea emarginata ang-u- 
lata (Sowerby) and a form of Lymnaea emarginata similar to that in 
Burt Lake. It almost appears that these shells may be compared 
in a crude manner with different kinds of liquids, which, when poured 
into differently shaped moulds (their environment), assume different 
shapes. 
Plate — . Map of northern end of Southern Peninsula of Michigan 
showing beaches of glacial Lakes Algonquin and Ni pissing. 2 
The cross-hatched portions show what was land during the time of 
the Algonquin highest beach level; the highest Nipissing beach is repre- 
sented by the line just inside the present lake shore and surrounding 
Mullet, Burt and Crooked Lakes. The • figures in the different lakes 
are their approximate hights above sea-level. The large squares repre- 
sent the townships, or areas six miles square. 
2 The data for this map was taken from the large map accompanying the paper by A. C. Lane: “Sum- 
mary of the Surface Geology of Michigan,” Rept. of the State Board of the Geol. Surv. of Mich, for the 
Yr. 1907; from the paper by F. Leverett mentioned above; and from corrections kindly made by Mr. 
Leverett from his field notes. 
