ARTHROPOD A — CRUSTACEA. 
97 
Fig. 48. — Isopods, fossil and recent, a, Palatga 
Carteri, Cenomanian Chalk, Dover ; b,Aega 
monophthalma from the Moray Firth. 
isopod, as also is the little Archaconimis Bradiei found in 
f[uautities in the Purbeck Beds of Wilts and Dorset. Several 
forms are found in Cretaceous and Tertiary rocks, as Palaega 
Carteri (Fig. 48) in the Cenomanian Chalk of Dover, and 
Eosphaeroma Sraithi 
in the Eocene of the 
Isle of Wight. One 
tribe of Isopoda, tlie 
Epicaridea, live as 
parasites on other 
Crustacea, notably on 
prawns, causing dis- 
tortion of their cara- 
paces. The distorted 
carapace seen in some 
specimens of Palaeoco- 
rystes, a crab from the 
Cambridge Green- 
sand, suggests that 
thev harboured tliese 
parasites. 
The Order Amphipoda contains the sand-hoppers and 
fresh-water shrimps; small animals with a body flattened 
from side to side, and with gills attached to the thoracic 
feet. A few have been found in Tertiary rocks, but are not 
represented in the Museum. 
The Order Stomatopoda comprises but a single family, 
the Squillidae, of which all living representatives are marine. 
Resembling lobsters in general form, they differ in having 
the carapace so short as to leave the hinder segments of the 
thorax uncovered, in having none of the thoracic limbs 
modified as jaws, but the first five pairs bearing pincer-claws 
which are especially large on the second pair, and in having 
gills borne only on the limbs of the abdomen. Hguilla, 
well-known in modern seas, is found in the London Clay, the 
Cretaceous of Lebanon, and the Kimmeridgian of Solenhofen 
(note the larval stages called Protozoea). Necroscilla, based on 
an abdominal fragment from the Middle Coal ^Measures of 
Derbyshire, is placed in this Order provisionally. 
The large Order Decapoda (lobsters, prawns, crabs) owes 
its name (ten feet) to the fact that the hinder five pairs of 
thoracic limbs are strongly developed as either walking or 
swimming legs or as pincers (k-o in Fig. 45) ; gills attached 
to these limbs are covered by the carapace. Three pairs of 
II 
Gallery 
VIII. 
Table-ease 
22 . 
Wall-ease 
13a. 
Table-ease 
22 . 
Table-eases 
22 20 . 
Wall-eases 
13a, 12o. 
