AETHEOPODA — CEUSTACEA. 



97 



G-allery 

 VIII. 

 Table-case 

 22. 



Fig. 48. — Isopods, fossil and recent, a, Palaega 

 Carteri, Cenomanian Chalk, Dover;; b,Aega 

 77ionophthah7ia from the; Moray Firth. 



isopod, as also is the little Archaeoniscus Brodiei found in 

 quantities 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 Smithi 

 in the Eocene of the 

 Isle of Wight. One 

 tribe of Isopoda, the 

 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 G-reen- 

 sand, suggests that 

 they harboured these 

 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. 

 Eesembling 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. Squilla, 

 well-known in modern seas, is found in the London Clay, 

 in the Cretaceous of Lebanon, and in the Kimmeridgian of 

 Solenhofen. 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 Table-cases 

 name (ten feet) to the fact that the hinder five pairs of -^aU cases 

 limbs are strongly developed as either walking or i3a, 12c. 

 swimming legs or as pincers (k-o in Eig. 45) ; gills attached 

 to these limbs are covered by the carapace. Three pairs of 



H 



Wall-case 



13A. 

 Table-case 



22. 



its 

 thoracic 



