THE 
GEOLOGICAL MAGAZINE. 
NEW SERIES. DECADE Ill. VOL. VI. 
No. V.—MAY, 1889. 
ORIGINAL ARTICLILEHS. 
I.—Own Fosstz Isopops, with A Description oF a New SpEcrEs. 
By James Carter, F.G.S, 
(PLATE VI. Figs. 1—7.) 
HE recent discovery in the Woodwardian Museum of an un- 
described species of Isopod from the Upper Greensand of 
Cambridge affords an opportunity for the revision of the entire list 
of that class of fossils. The total number of species which have 
hitherto been described as occurring in a fossil state is inconsider- 
able,—probably scarcely thirty—including both foreign and British. 
To what extent this small number expresses the variety of specific 
form of this tribe of Crustaceans, which actually existed during 
the period of deposition of the several rocks in which their remains 
occur, it is impossible to determine, as doubtless by far the greater 
proportion of the individuals perished by reason of the delicacy of 
their tissues—the larger and thick-shelled species only having been 
preserved—the small, thin-shelled kinds not admitting of recogniz- 
able ‘‘fossilization.” Specimens of Jurassic and Cretaceous Isopods 
are very rare both as to variety and individual number, and it may 
be inferred that this rarity of occurrence results from the more or 
less turbulent conditions under which these marine deposits were 
formed. The Tertiary estuarine and freshwater species, buried under 
more tranquil conditions, are much better preserved, and occur in 
some localities in innumerable abundance—Spheroma, Archeoniscus, 
ete. 
The succession and geological distribution of Isopods, so far as has 
yet been ascertained, is indicated by the following list :— 
One species has been obtained form the Old Red Sandstone. 
? One ,, Be the Triassic rocks. 
Five ,, is the Jurassic _,, 
Three ,, a the Cretaceous ,, 
Highteen the Tertiary ,, 
9? 
About three-fourths of the forms enumerated are foreign, and seven 
species have been recorded by Dr. Woodward as occurring in this 
country :— 
Prearcturus gigas, H. Woodw. ... ... ... Old Red Sandstone, Hereford. 
Archeoniscus Brodiei, Milne Edwards ... ... Purbeck Beds, Vale of Wardour. 
‘D Edwardsii, H. Woodw. ‘ on Re 
Palega Carteri, H. Woodw. ... ... ... ... Grey Chalk, Dover. 
Bopyrus sp. (parasitic) ... ... ... ... ... Greensand, Cambridge. 
Lospheroma fiuviatile, H. Woodw.... ... ... U. Eocene, Isle of Wight. 
Smithii, H. Woodw.... ... ... 90 99 
3? 
DECADE III.—VOL. VI.—NO. Y. 13 
