STATE GEOLOGIST. 119 



GENUS Cyzicus. 



(Am not familar with any description of the p^eneric characters.) 

 Remarks on the Sub-Order. — The species of this sub-order are scattered rather 

 sparingly over the world, and many of them are dependent on peculiar circum- 

 stances for their perfect development, as in the case of Artemia (or Brine Shrimp) 

 which is found in the waters of salt lakes and in the brine tubs of salt manu- 

 factories. 



Of the family Arteiniadce several species occur throughout the United States. 

 No Chirocephalus has been found west of the Rocky Mountains. Artemia occurs 

 in many places, as, one in Great Salt Lake, one in Mono Lake, California, and 

 one in the eastern U. S. The genus BrancMnectas which has a representative in 

 Greenland and in Labrador, has also a species in Colorado, 12,800 feet above the 

 sea. I am not informed that any species of Nebalia occurs in North America. 



The tribe Lhnnadioidea is without a known representative east of the Missis- 

 sippi and north of San Domingo. But in Greenland and the arctic regions, 

 Lepidurus glacialis is found. West of the Mississippi and east of the Rocky 

 Mountrins are three species of Apiis, and there has been another found on the 

 Pacific, at Cape St. Lucas. Geologically, the genus is found in European rocks 

 in the Triassic, and our own rocks will probably furnish species. 



In the Phyllopoda the abdomen and thorax are merged together, and in all 

 but the family Artemiadce, there is a large carapace covering most of the body. 

 In the Limnadidoe this shell is large and double, and resembles the small Cyclas 

 shells of fresh water, and are often collected by Conchologists as such. The eggs 

 are round or polygonal, and are dense and tough-^shelled. The eggs are carried 

 in an ova-sack similar to that of Cyclops, or in the Limnadiadce. They are borne 

 under the shell, as in Daphnia, etc. The young, as in other Entomostraca, 

 hatch from the egg in the *' Nauplius stage" described more particularly under 

 Cyclops. The difference between the sexes is usually sharply defined. The pro- 

 cess of reproduction is very interesting in many species of this sub- order. The 

 normal method of reproduction is perhaps less common than what is known as 

 parthenogenesis, or virgin reproduction. The eggs are produced by a simple 

 budding process from the ovary, without fertilization by the male. Tiie propor- 

 tion of males to females is very small. In some localities the males are entirely 

 absent. In Artemia the amount of saline matter in water seems to vary the 

 comparative number of males. This affords a curious parallel with the sexual 

 changes in the pupa of the honey bee. The saltness of the water not only affects 

 the young, the form of the parent also varies. Schmankiewitsch found near 

 Odessa, Russia, a species of Artemia, and by studying it discovered that it 

 changed its form to correspond with the greater or less saltness of the water. 

 Toward the end of the summer, when the rain and cold weather set in, the 

 Artemia increases in size, and the July generation has many differences from the 

 later ones. Ho then attempted to verify his observations by artificial breeding. 

 He increased the concentration in one case and lowered it in the other, and 

 found that after a series of generations the two sets of animals varied between 

 themselves, and also both differed from those of the pond from which they came. 

 He also learned that males were only produced in water of medium strength. 



In the genus Apus similar parthenogenetic broods are produced. Siebold's 

 experiments, which have been made with great care and minuteness, have estab- 

 lished this fact beyond doubt. 



