330 THE AMERICAN NATURALIST. [VoL. XXXIV. 
number of species the new shell is usually as large as the older one, 
and when differences do occur, they are but slight and as often 
present larger shells as ‘they do smaller ones. The differences in 
size among the individuals of a given species in one locality are 
usually small, the greatest number presenting the medium dimen- 
sions, while dwarfs and giants are equally rare. These extremes are 
examples of variation within the species and cannot represent the 
young and the old — the extremes of a growth series. The instances 
cited by Rhumbler of great differences in size are explained by the 
supposition that more than one species has been included in the 
series, the author contending here, as elsewhere, for the recognition 
of a greater number of species in this group. The process of repair, 
local growth about the mouth, resolution of the shell, and exuviation 
are none of them regarded as proofs of the growth of the shell as a 
whole. The author's extended observations on the Rhizopoda thus 
lead him to confirm the views of Verworn. C A E. 
Abyssal Rhizopoda. — Dr. E. Penard has recently published! an 
account of his interesting studies upon the Rhizopoda from the bot- 
tom of Swiss lakes. His attention was given to collections of the 
bottom ooze, from which he describes a characteristic fauna of 
peculiar species. Many of these are new, differing from the littoral 
species to such an extent as to necessitate, in the author's estimation, 
varietal or specific distinction. In numbers they exceed the strag- 
glers from the shore fauna which occasionally invade the depths. 
The author does not favor the view that the Rhizopoda are some- 
times pelagic in habit, and suggests that their floating is due to the 
gases of putrefaction. This is certainly not the case in some Ameri- 
can waters where their numbers and activity entitle them to rank as 
planktonts. The abyssal Rhizopoda are most abundant at depths of 
25-50 meters, being modified by shore contamination above that 
limit, and decreasing in numbers below it. Their distribution is 
widespread, though irregular as to species. During the winter sea- 
son they decline in numbers as their food, the diatoms, is at a mini- 
mum at that time. In addition to the Léman, eight other Swiss lakes 
were explored, and the same types of abyssal Rhizopoda were found 
in all of them. This fauna, living under almost unchanging con- 
ditions of great pressure, low temperature (about 4? C.), little or 
no light, no currents, and little food but diatoms, exhibits certain 
!Penard, E. Les rhizopodes du Lac Léman. Rev. Suisse de Zoöl., tome vii, pP- 
1-142, Pls. I-IX, 1899. 
