Marsh — 2^ortli American Species of Diaptonius. 403 



appendicibus tentaculifonnibus 2 ininiinis instructiis. Anten- 

 nae primi paris articulis 25 apicem versus parum longitudine 

 crescentibns compositae; dextra maris articulatione inter ar- 

 ticulum 18-mum. et 19-muni geniculans, antecedentibus 6-tumi- 

 dis, sequeiitibus 5 in 2 iiiodo confluentibus articnlas. Ramus 

 antennarmn 2-di paris exterior interiore longior 7-articulatus, 

 articulo ultimo omnium maximo setisque longissimis apicalibua 

 instructo ; setae articulis antecedentibus inhaerentes breves 

 et fere equales. Maxillae 2-di paris 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 sequeutibus 3-articulato pedes ultimi 

 paris ceteris dissimiles 5-articulati, articulo 2-do intus appe3>- 

 dice parva vel rudimento rami interioris instructo ; in f emina 

 breves inter se equales, articulo ultimo perbrevi et rudimentari, 

 penultimo sine fine in unguem validum iutrorsum curvatmn 

 exeunte; dexter maris subcheliformis, articulo ultimo in un- 

 guem mobilem longissimmn conformato. Oculus unicus." 



A^^ALYTICAL KEYS. 



Artificial keys are always unsuasiaciorj, 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 tiie 

 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, 

 ^o 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. 



