Marsh—North American Species of Diaptomus. 383 
seems unfortunate that so many papers on plankton list the 
Diaptomi simply under the generic name without an attempt 
to distinguish species, thus detracting much from the value of 
the observations, inasmuch as the Diaptomi have very distinct 
individual peculiarities, and react very differently to their 
environments. 
With this in view, the author has attempted to provide suffi¬ 
cient figures of each species so that its identity cannot he a 
questionable matter. The original plan involved personal ac¬ 
quaintance with each species, and figures from specimens actu¬ 
ally in the collections studied. It was found impossible, how¬ 
ever, to carry this out in every case; for example, it was found 
impossible to get material of D. novamexicanus , as Herrick 
had preserved none of the original material. The papers de¬ 
scribing Pearse’s species Wardi and spatulocrenatus were re¬ 
ceived while this paper was in press and after the plates had 
been made, so that it was impossible to provide figures, or to do 
much more than to give the species their proper place in the 
classification. So, in other cases, because of imperfect catalog¬ 
ing of museum material, it was impossible to get specimens of 
the animals originally studied. Therefore, in some cases, it has 
been found necessary to reproduce the original figures of the 
authors of the species. Most of the figures, however, are from 
material in the collection of the author. 
As the result of studies on other collections, it is hoped, be¬ 
fore many years, to supplement this work, so that we may get 
more nearly a synopsis of all the North American species. 
Meanwhile it is to be expected that intermediate forms will be 
discovered which may change materially the specific limits as 
they appear at the present time. 
The author would express his grateful acknowledgment to 
all who kindly aided in this work by assisting in making the 
collections on which it is based. To the following he has been 
especially indebted: to Professor E. A. Birge of the Univer¬ 
sity of Wisconsin, not only for the exchange of material from 
Wisconsin, but for extensive collections made in the southern 
states; to Professor Chauncey Juday of the University of Cali- 
