to their environment; habits,' — subjects no- 

 where treated under a separate heading ; and 

 all reference to the long appendix is omitted. 



About a fourth of the entire work is devoted 

 to the systematic account of the species and 

 higher groups of Ph^dlopoda, regarded b}' Pro- 

 fessor Packard as a sub-order of Branchiopoda, 

 which is made to include Cladocera and Ostra- 

 coda also. The Phyllopoda are divided as 



follows into families and sub-families, which 

 include the number of recognized North- 

 American genera and species nearly as indi- 

 cated : — 



LiMNADIIDAE : 



Limnetinae (1 genus, 4 species). 



Estheriinae (3 genera, 11 species). 

 Apodidae (2 genera, 9 species) . 

 Branchipodidae : 



Branchipodinae (5 genera, 12 species). 



Thamnocephalinae (1 genus, 1 species). 



All the groups are described ; nearly all the 

 species are figured, many of them verj' fully ; 

 and important notes on variabilit}' and habits 

 are given for some of the species. Artemia 

 gracilis is treated moi-e at length than any 

 other species, and is made to include all the 

 described North-American species ; but, in re- 

 gard to its relation to the European A. salina, 

 tiiere is certainly confusion, as the following 

 paragraphs show. 



" Upon comparing our species with the Eu- 

 ropean, it is difficult to find good diflf'erential 

 characters, as the portions of the body where 

 specific diflTerences would be expected to occur 

 are liable to considerable vaiiation. Upon 

 comparing a number of females from Great 

 Salt Lake with a number of females of the 

 maleless generation from Trieste, Austria, 

 received from Professor Siebold, there are 

 really no diflTerences of importance. Our A. 

 gracilis (Verrill's fertilis) is slighter, with a 

 smaller head ; and perhaps the second antennae 

 are a little slighter in build ; I see no essen- 

 tial diflJ'erence in the form of the ovisac, while 

 the shape of the legs, especially the sixth en- 

 dite, is essentially the same " (p. 331). 



" On comparing a number of Salt Lake fe- 

 males with individuals of the same sex of the 

 European Artemia salina, our species was 

 found to be undoubtedly specificall}^ distinct ; 

 the Utah specimens are slenderer, smaller, and 



