362 GEOLOGICAL SURVEY OF THE TERRITORIES. 
“Classen und Ordnungen der Thierreichs” ) suggests that the Lernzans 
might have infested Paleozoic fish, and on general grounds we should 
think that they probably extended as far back as the primordial 
zone, inasmuch as highly developed Trilobites and Ostracodes appear 
there. Ano'ther argument is the interesting discovery made in 1865, 
by Mr. Woodward, of the Cirripede Turrilepas Wrightit from the 
Wenlock limestone and Dudley shale of the Upper Silurian formation. 
Previous to this, according to Woodward, ‘the oldest known Cirripede 
was the Pollicipes rheticus from the Rheetic beds of Somersetshire”; 
while tiie type is not uncommon in the Cretaceous, and has flourished 
from that period to the present. 
Of the Merostomata the oldest group is the Eurypterida, the Xipho- 
sura not dating beyond the Lower Carboniferous. The Eurypterids 
have not been found below the Upper Silurian (Lower Helderberg in 
America), and the aberrant forms Hemiaspis, Bunoddes, Pseudoniscus, 
and Exapinurus are Upper Silurian forms. Among the Xiphosura, 
Cyclus, the lowest form, is found in the Carboniferous, and ranges, ac- 
cording to Woodward, as far up as the Permian. In the same period 
occur Bellinurus, Prestwichia, and Euproéps, being in this country 
found in the lower part of the true Coal-measures, and associated in the 
same beds with Ceratiocaris, Hurypterus (Anthraconectes and certain 
Isopoda and Macrurous Decapoda (Anthrapalemon). The genus Limu- 
lus first appears in the Jurassic, and the species differ but shghtly from 
those now living. 
The more typical Phyllopeda made their appearance during the Triassic 
period. The lowest group, however, the Estheriade, appeared during the 
Devonian, a species referred to Estheria being found in that formation in 
Kurope. The Cladocera are not known to have existed previous to the 
Tertiary period, and it was not until recently (1862) that Von Hayden 
discovered the ephippium of a Daphnia in the Rheinish brown coal 
(Gerstaecker, in Bronn’s Klassen und Ordnungen, We.), said by Lyell 
to be of Eocene age. It should be noticed, however, that the fossil be- 
longs next to Sida, the most highly organized genus of the group, and 
as it is not unlikely that such pelagic forms as Nvadne may have existed 
in the Mesozoic seas, if not earlier, [ have ventured to run the point of 
the wedge into the Carboniferous period. 
The Apodidez date back to the early part of the Mesozoic, a Triassic 
species of Apus having been found in Europe, according to Mr. Salter. 
HI.—GHOGRAPHICAL DISTRIBUTION. 
(With a map.) 
The materials for the thorough study of the geographical distribution 
of the Phyllopod Crustacea of North America, as indeed of any other 
of the continents, perhaps not excepting Huropeo- Asia, are quite scanty. 
The exceptional habits of the members of this suborder, their usual 
rarity or periodical occurrence, and their very local distribution, have 
caused them to escape the observation of most collectors, and to be found 
more by accident than as the result of well-matured plans of search. 
The salient points in the distribution over the globe of the Phyllopods 
are as follows; although the conclusions here presented are, of course, 
provisional, and much - yet remains to be discovered as to the distribu- 
tion of these interesting forms. 
It will be seen by reference to the lists presented in the following 
pages that a large proportion of our North America Phyllopoda, includ- 
ing nearly all the species of Hstheria, are restricted to the elevated dry 
central zodgeographical province of the United States, and adjacent 
