Crustacea — Malacostraca. 83 



3. — Macrouea. To this section belongs the Lobster, Prawn, and Crustacea. 

 Shrimp, with their numerous allies. They have stalked eyes ; CrALIEBY 

 the cephalothorax bears five pairs of walking-legs; they have jjg^g^ gj^g 

 a well-developed pleon or abdomen, ending in a broad tail-fan for wall-casea 

 swimming ; the branchige are placed beneath the overarching 12-14, 

 cephalothorax at the bases of the walking-legs. The oldest known cases" 

 membc r of this division is the Palceopalcbmorh Newberry i from the 80-85. 

 Tipper Devonian of Ohio, U.S. Other early forms are met with 

 in the Coal-measures, as the Anthrapalamon HussellianuSy A. Farkii, 

 A. Traquairii, A. Etheridgei (Fig. 143). Another characteristic 

 group is that of the Eryonidce^ abundantly represented from the 

 Trias of Bohemia to the Neocomian of Silesia. Several allied 

 genera were discovered living in deep water and dredged by the 

 "Challenger" Expedition in the Mediterranean, Atlantic, and 

 Pacific, from 220 to 1,900 fathoms. The recent species closely 

 resemble their Oolitic and Liassic ancestors. (See Fig. 141, 5.) 



The genera JEger, Penceus, etc., were well represented in the 

 Jurassic rocks, and Callianassa from the Oolites to the Tertiaries. 

 (See Fig. 142.) 



Fig. 144. — Palceinachus longipes, H. "Woodw. Great Oolite : "Wiltshire. 



4. — Brachtura. This division embraces the '' short- tailed" 

 crabs, in which the abdomen is usually quite small and entirely 

 hidden beneath the expanded carapace or cephalothorax ; only in 

 certain anomalous forms is the pleon, or abdomen, seen to project 

 behind the cephalothorax. 



True crabs first make their appearance in the Great Oolite, the 

 oldest known crab being the PalainacJius longipes (H. Woodw.), 

 from Wiltshire, which has the limbs also preserved (Fig. 144). 

 Numerous small carapaces referred to the genus Prosopon occur in 

 the Upper White Jura of Germany, and one in the Stonesfield Slate. 



