PACKARD.) 



PHYLLOPOD CEUSTACEA OF NORTH AMERICA. 617 



West of the Mississippi, three species are known to inhabit the region 

 east of the Kocky Mountains, and a fourth has occurred on the Pacific 

 slope at Cape Saint Lucas. 



Of the I'amily Branch ijjodidce, species occur scattered over the whole 

 country, though no BrancJiipus has yet been discovered in the Pacific 

 (States. An Artemia occurs in Mono Lake, California, and the Great 

 Salt Lake. The genus Branchinectes, with one species in Greenland and 

 another in Labrador, is also represented by an interesting form in Colo- 

 rado, at an elevation of 12,500 feet. 



Of the family lAmnadiadw, species occur scattered over the whole 

 country, east and west of the Eocky Mountains, in British America, and 

 the West Indies. In the Pacific States, but one species {Estheria Call- 

 fornica, Pack.) has occurred, and that is very unlike any eastern species 

 as yet discovered, and closely resembles an Italian species, thus bearing 

 out the analogy of the Pacific coast fauna to that of Europe. 



The geological distribution of the fresh-water phyllopods is exceed- 

 ingly interesting. The oldest forms are the Ustherice, which occur as 

 low down as the Devonian formation in Europe, while certain forms in 

 the Mesozoic beds of this country havebeen described as bivalve mollusks. 

 The genus A2nis occurs in European Triassic rocks. The fresh-water 

 strata of Mesozoic and Tertiarj- age, especially in the West, will undoubt- 

 edly, when thoroughly explored, reveal some of thgse forms, and the 

 attention of paleontologists and collectors is hereby drawn to them. 



The habits of these crustaceans are exceedingly interesting from their 

 unusual dependence on physical surroundings. They usually abound 

 in pools and puddles that dry up in warm weatiier; when the pools are 

 filled, after a series of heavy rains, they suddenly appear. They are very 

 local, rarely met with, but when they do occur, exist in large numbers. 

 This singular appearance after rains, in the beds of pools that have 

 dried up, is due to the wonderful vitality of the eggs, which are sur- 

 rounded by a dense outer shell, enabling them to resist great changes in 

 temperature, and to be dried up for months without iojury. Thus the 

 eggs dropped in the bottom of pools and left there during the hot sum- 

 mer-months, when the pool is dried up, survive the exposure to the sun 

 and the cold of winter to hatch out in the spring. Dr. Brauer, of 

 Vienna, believes, as he has informed me, from certain experiments ou 

 Ustheria, that the eggs would live and hatch if kept in dry mud for 

 several years. Artemia. which lives in salt-water, can be reared by 

 putting the eggs in fresh water. And here I would ask any one who i& 

 so situated to send me a quantity of mud from the banks of Salt Lake, 

 Utah, containing their eggs; the mud taken from the edge of the lake,, 

 at any season, must teem with their eggs, and it could be dried and sent 

 east by express. On receiving it, and i)laciug the mud in fresh water, 

 this interesting animal can be reared and studied at leisure. We have 

 seen that these creatures, in one species, at least, like the plant-lice, re- 

 produces parthenogenetically at one season, and by the normal mode at 

 another, and thus some of the most interesting questions in biology may 

 be studied, and perhaps settled by a thorougb study of the mode of life 

 of these interesting creatures. 



I append a brief synopsis of the fresh-water species of America north 

 of Mexico, beginning with the lowest forms, so that they may be readily 

 identified ; and I hope, by drawing the attention of individuals and 

 government surveying i)arties, especially in the Far West, to these in- 

 teresting animals, to have their co-operation in the preparation of a 

 monograph of the group. Specimens should be collected by hundreds, 

 as they always occur in great abundance when found at all, and placed 

 in strong alcohol for permanent preservation. 



