Marsh—North American Species of Diaptomus. 403 
appendicibus tentaculiformibus 2 minimis instructus. Anten¬ 
nae primi paris articulis 25 apicem versus parum longitudine 
crescentibus compositae; dextra maris articulatione inter ar- 
ticulum 18-mum et 19-mum geniculans, antecedentibus 6-turni- 
dis 5 sequentibus 5 in 2 mode confiuentibus articulos. Ramus 
antennarum 2-di paris exterior interiore longior 7-articuiatus, 
articulo ultimo omnium maximo setisque longissimis apicalibus 
instructo; setae articulis antecedentibus inhaerentes breves 
et fere equales. Maxillae 2-di pails breves et crassae; 3-tii 
paris elongatae et antice vergentes 7-articulatae setisque brevi- 
bus obsitae. Pedes anteriores 8 biramosi natatorii, ramo inter¬ 
iore in 1-mo pari 2-, in sequentibus 3-articulato pedes ultimi 
paris ceteris dissimiles 5-articulati, articulo 2-do intus appen- 
dice parva vel rudimento rami interioris instructo; in femina 
breves inter se equates, articulo ultimo perbrevi et rudimentari, 
penultimo sine tine in unguem validum introrsum curvatum 
exeunte; dexter maris subcheliformis, articulo ultimo in un¬ 
guem mobilem longissimum conformato. Oculus unicus.” 
ANALYTICAL KEYS. 
Artificial keys are always unsatisfactory, and yet they seem 
necessary in order to help one to a determination of species. 
In the following keys an attempt has been made to indicate 
the groupings of species by a few salient points. The result 
is not what could be wished, but it is hoped that it will be of 
assistance, especially to those who are not familiar with the 
classification of the genus. The synopses of DeGuerne and 
Richard are by all odds the most satisfactory of those hitherto 
published; accordingly these analyses are based on their work. 
Ro attempt has been made to carry the analysis of the charac¬ 
teristics of the females far enough to determine all the species, 
for it is impossible, in some cases, to separate the females of 
related species. A final determination can be made only when 
one has the male forms. 
