34 CRUSTACEA BRANCHIOPODA CHAP. 



the sea ; Apus cancriforrnis has, however, been found in Armenia 

 at 10,000 feet above sea-level. 



Wells and underground waters do not generally contain 

 Phyllopods ; but a species of Brancliipus and one of Limnetis, 

 both blind, have been described from the caves of Carniola. 



One of the many puzzles presented by these creatures is the 

 erratic way in which they are scattered through the regions they 

 inhabit ; a single small pond, a few yards or less in diameter, 

 may be the only place within many miles in which a given species 

 can be found ; in this pond it may, however, appear regularly 

 season after season for some time, and then suddenly vanish. 



Geographically, the Phyllopoda are cosmopolitan, represen- 

 tatives of every family and of some genera (e.g. Streptocephalus, 

 Lepidurus, Estheria} being found in every one of the great zoo- 

 logical regions, though a few aberrant genera are of limited range, 

 thus Polyartemia is known only from the northern Palaearctic 

 and Nearctic regions, Thamnoceplialus only from the Central 

 United States. The genus Artemia is not at present known in 

 Australia. 1 The only recorded British species are Chirocephalus 

 diaphanus, Artemia salina, and Apus cancriformis, 2 but other 

 continental islands, for example the West Indian group, are 

 better supplied. The distribution of the species is very im- 

 perfectly known, but on the whole every main zoological region 

 seems to have its own peculiar species, which do not pass beyond 

 its boundaries. Brancliinecta paludosa and Lepidurus glacialis are 

 circumpolar, both occurring in Norway, in Lapland, in Greenland, 

 and in Arctic North America ; but with these exceptions the 

 Palaearctic and Nearctic species seem to be distinct. The Euro- 

 pean species Apus cancriformis occurs in Algiers, but the relations 

 between the species of Northern Africa as a whole and those of 

 Southern Europe on the one hand, or of Central and Southern 

 Africa on the other, have yet to be worked out. 



The soft-bodied Branchipodidae are not known in the fossil 

 condition ; 3 an Apus, closely related to the modern A. cancriformis, 

 has been found in the Trias, but the most numerous remains have 

 been left, as might be expected, by the hard-shelled Limnadiidae ; 



1 Sayce has since described it, Proc. Roy. Soc. Victoria, xv., 1903, p. 229. 



2 A. cancriformis had been supposed to have disappeared from the British fauna 

 for many years, but it was found in Scotland in 1907. See R. Guriiev, Xaturc, 

 Ixxvi., 1907, p. 589. 



3 Branchipodidcs has been described by H. "Woodward, from Tertiary strata. 



