ii GENERA OF PHYLLOPODA 35 



carapaces, closely resembling those of the modern Extln'ria, 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 ranpre of environmental conditions. 



o 



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 nnjointed in the female, jointed and prehensile in 

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

 lH-aring 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 



wdl formed, their margins set<e. 



liriic]iin<rt<i. Yen-ill Second antennae of <$ without lateral 

 appendages ; ovisac of $? elongated. B. pnlm!"*!, 0. F. 

 1M nil. Circnmpolar. 



I!i-<iiir]i)i>}ii-i<l<ii>xis, G. O. Sars 2 Second antennae of J as in 

 Branchinecta : ovisac of 9 *hort. R hodysoni, G. O. Sais 

 Cape of Good Hope. 



BrancJwpus, Schaell'er Second antennae of <$ with simple 

 internal filamentous appendage. /;. .-/</;///<///., Linn. 

 Central Europe. 



Hr>'))tocephaln*, I laird Second antennae of J ^-jointed, tin- 

 last joint bifid ; an external lilaiiientoiis appendage. 

 torrirnnii^. \Yagn., 1'oland. 



Chiriicfjilniltix, I'revost Second antenni f ' 3-jointed, with a 



jointed internal appendage, which bears secondary pi 



four cylindrical and one lamellar. <'. >1 !<ij^<' n n.^ Provost 



(Fig. 2, p. 20). Britain, Central Kurop.-. 



b. Abdominal segments live or fewer, and a tel.-oii. Anal I 



small or 0, sparsely or not at all setose. 



Artemia, l,ea<-h Second antennae of < ' \\iihout hlam.-niou- 



1 Consult I'.aird, " Moiiograpli ul' tin- i;r;tiifhi<>|mdH,i 

 p. 18. Packard. 12th Ann. J,:-/>. ''.,s r . Geol. Survey, ]>;irt L, 1879. 



- .Irch.f. Math, or, Nitturvidensk: xx., 1898, N"-. 1 ami i). Thiule, 

 System, xiii., 1900, p. 563. 



