Marsh—North American Species of Diaptomits . 401 
Illinois south, while D. conipedatus is found only in the South. 
Here again is pretty clear evidence of the importance of the 
factors of water carriage and temperature. 
The signicauda group is confined to the mountain region of 
the West, and I assume it to be a product of isolation. There 
is no evidence of the effect of temperature in the distribution 
of the members of this group. 
The albuquerquensis group is distinctly southern. D. sal- 
tillinus, the most aberrant member of the group, is found as far 
north as Nebraska and as far south as Florida, if I am cor¬ 
rect in supposing that D. albuquerquensis Schacht is D. saltil- 
linus Brewer. The distribution of this group, as in the case 
of the others, gives distinct evidence of the effect of latitude. 
Both Forbes and Ward, following European authors, have 
thought that elevation was a controlling factor in the distri¬ 
bution of fresh water organisms. So far as Diaptomi are con¬ 
cerned, I see no reason for thinking that elevation has any ef¬ 
fect in controlling the distribution of our American species, 
except in the indirect way that elevation is accompanied by 
low temperature. It seems clear to me that the species of Di¬ 
aptomi are commonly confined within rather narrow limits of 
temperature. 
diaptomus Westwood. 
1785. Cyclops O. F. Muller. 
1820. Monoculus Jurine. 
1836. Diaptomus Westwood. 
1838. Cyclopsina Milne-Edwards. 
1838. Glaucea Koch. 
1848. Cyclops Nicolet. 
1889. Diaptomus De Guerne and Richard. 
1897. Diaptomus Schacht. 
Although the number of described species of Diaptomus has 
greatly increased since the publication of De Guerne and Rich¬ 
ard’s Revision, and it might be thought wise to subdivide the 
genus, it has not seemed to me best. The description as given 
by them is exact, and it seems undesirable to make any change 
in it. 
26 — S. & A. 
