Bibliographical Notices. . 201 
Ceratiocaris, Peltocaris, Dictyocaris, &e. to Nebalia, has given us a 
series of sketches showing graphically the geological succession of 
this group and the Estheriade. MHymenocaris, which Salter regards 
as the more generalized type, lived during the primordial period ; 
Peitocaris and Discinocaris (Woodward) characterize the Lower 
Silurian period; Ceratiocaris the Upper ; Dictyocaris the Upper 
Silurian and lowest Devonian ; Dithyrocaris and Argas the Carbo- 
niferous. No Mesozoic member of the family has yet been dis- 
covered; but as there are several species of Nebalia now living in 
our seas, it is reasonable to suppose that the type has existed in an 
unbroken succession from primordial times until now. The Palzxo- 
zoic species were giguntic 1n size, some being a foot or more in length 
(the carapace of Dithyrocaris pholadomya, Salter, was seven inches 
long), while our recent Nebalia is less than an inch in length. 
‘The Potsdam Sandstone also contains the remains of a third 
grand division of the Entomostraca, the Ostracoda, remains of 
Leperditia having been found in Canada as well as in the Lower 
Silurian of Europe. 
“‘ No fossil Copepoda have yet been discovered; but we should 
scarcely wonder at this, owing to their soft bodies. Gerstiicker (in 
Bronn’s ‘ Klassen und Ordnungen des Thierreichs’) suggests that 
the Lerneans 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. Another argument is the interesting 
discovery, made in 1865 by Dr. H. Woodward, of the Cirripede 
Turrilepas Wrightiana, 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 rheti- 
cus from the Rheetic beds of Somerset, while the type is not uncom- 
mon in the Cretaceous, and has flourished from that period to the 
present. 
“ Of the Merostomata the oldest group is the Eurypterida, the 
Xiphosura not dating beyond the Lower Carboniferous. The Euryp- 
terids have not been found below the Upper Silurian (Lower Hel- 
derberg 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 Carbonife- 
rous, and ranges, according to Woodward, as far up as the Permian. 
In the same period occur Bellinurus, Prestwichia, and Euprodps, 
being in this country [North America] found in the lower part of 
the true Coal-measures, and associated in the same beds with Cera- 
tiocaris, Eurypterus (Anthraconectes), and certain Isopoda and 
Macrourous Decapoda (Anthrapalemon). The genus Limulus first 
appears in the Jurassic ; and the species differ but slightly from those 
now living. 
“The more typical Phyllopoda made their appearance during the 
Triassic period. The lowest group, however, the Estheriads, ap- 
peared during the Devonian, a species referred to Estheria being found 
in that formation in Europe. The Cladocera are not known to have 
existed previous to the Tertiary period ; and it was not until recently 
