ii GENERA OF PHYLLOPODA 35 



carapaces, closely resembling those of the modern Estheria, are 

 known in beds of all ages from the Devonian period to recent 

 times ; these carapaces are in several cases associated with fossils ' 

 of an apparently marine type. None of the fossil species differ 

 in any important characters from those now living, so that the 

 Phyllopoda have existed in practically their present form for 

 an enormously long period ; this fact, and the evidence that 

 species of existing genera were at one time marine, explain the 

 wide distribution of animals at present restricted to a remarkably 

 limited range of environmental conditions. 



Summary of the Characters of the Genera. 



SUB-ORDER PHYLLOPODA. Branchiopoda with an elongated body, pro- 

 vided with at least ten pairs of post-cephalic limbs, the heart extending 

 through four or more thoracic segments, and having at least four pairs of ostia. 



Fam. 1. Branchipodidae. 1 Carapace rudimentary, eyes stalked ; the 

 second antennae flat and unjointed in the female, jointed and prehensile in 

 the male ; female generative opening single ; telson not laterally compressed, 

 bearing two flattened lobes, or none. The heart extending through the 

 thorax and the greater part of the abdomen. 



A. Eleven pairs of praegenital ambulatory limbs. 



a. Abdomen of six well -formed segments and a telson; anal lobes 



well formed, their margins setose. 



Branchinecta, Yen-ill Second antennae of <$ without lateral 



appendages ; ovisac of <j? elongated. B. paludosa, 0. F. 



Mull. Circumpolar. 

 Branchiopodopsis, G. 0. Sars 2 Second antennae of $ as in 



Branchinecta ; ovisac of $ short. . hodysoni, G. O. Sars 



Cape of Good Hope. 

 Branchipus, Schaeffer Second antennae of $ with simple 



internal filamentous appendage. B. stagnalis, Linn. 



Central Europe. 

 Streptocephalus, Baird Second antennae of $ 3-jointed, the 



last joint bifid ; an external filamentous appendage. S. 



torvicornis, Wagn., Poland. 

 Chirocephalus, Prevost Second antennae of $ 3-jointed, with a 



jointed internal appendage, which bears secondary processes, 



four cylindrical and one lamellar. C. diaphanus, Prevost 



(Fig. 2, p. 20). Britain, Central Europe. 



b. Abdominal segments five or fewer, and a telson. Anal lobes 



small or 0, sparsely or not at all setose. 



Artemia, Leach Second antennae .of $ without filamentous 



1 Consult Baird, " Monograph of the Branchiopodidae," Proc. Zool. Soc. 1852, 

 p. 18. Packard, 12th Ann. Rep. U.S. Geol. Survey, parti., 1879. 



2 Arch. f. Math, og Naturvidensk. xx., 1898, Kos. 4 and 6. Thiele, Zool. Jahrb. 

 System, xiii., 1900, p. 563. 



