Marsh — North Ameiican Species of Diaptomus. 4:01 



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 ot 

 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 albuque?'quensis group is distinctly southern. D. scd- 

 tillinus, the most aberrant member of the group, is found as far 

 north as Xebraska and as far south as Florida, if I am cor- 

 rect in supposing that D. alhuquerquensis 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 Diaptotni are con- 

 cerned, I see no reason for thinking th&t 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. Miiller. 



1820. Monoculus Jurine. 



1836. Diaptomus Westwood. 



1838. Cyclopsina Milne-Edwards. 



1838. Glaucea Koch. 



1848. Cyclops l^icolet. 



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. 



