524 ZOOLOGY SECT. 



small : the bases of the antennules are sunk in pits of the carapace, 

 and the antenna has no exopodite. The third maxillipedes are 

 flattened and valve-like. 



Including the true crabs, such as Cancer, Maia, Dromia, &c. 



(Figs. 427 and 428). 



ORDER 4. STOMATOPODA. 



Tlmracostraca of considerable size in which the three posterior 

 thoracic segments are not covered by the carapace. The abdomen 

 is very large. The five anterior thoracic limbs are maxillipedes, 

 and the second of them is very large and forms a defensive weapon : 

 the last three are small biramous legs. The gills are borne on the 

 abdominal segments. The eyes are stalked. 



Including Squilla and Gonodactylus (Fig. 429). 



ORDER 5. CUMACEA. 



Small shrimp-like Malacostraca having the first three or four 

 thoracic segments fused with the head, the rest free. The two 

 first pairs of thoracic appendages are maxillipedes, the remaining 

 six legs ; some of the latter are biramous. The eyes are sessile. 



Including Cuma, Diasiylis, &c. (Fig. 430). 



ORDER 6. ARTHROSTRACA. 



Malacostraca in which the first, sometimes also the second, 

 thoracic segment is fused with the head and bears maxillipedes : 

 the remaining seven are free and bear legs. The eyes are usually 

 sessile. 



Sub-order a. Amphipoda. 



Arthrostraca in which the body is usually compressed or flattened 

 from side to side. The gills are borne on the thoracic ap- 

 pendages. 



Including Gammarus (Fresh-water shrimp), Orchestia (Saiid- 

 hopper), Phronima, Gaprella, Cyamus (Whale-louse), &c. (Figs. 431 

 and 433). 



Sub-order b. Isopoda. 



Arthrostraca in which the body is usually depressed or flattened 

 from above downwards. The gills are borne on the abdominal 

 appendages. 



Including (a) free forms Asellus, Oniscus (Wood-louse), Arma- 

 dillo (Pill-bug) ; (ft) parasitic forms Cymothoc, Bcpyrus, &c. (Figs. 

 432 and 434). 



Systematic Position of the Examples. 



The genera Apus and Lepidurus belong to the family Apodidce, 

 sub-order Euyhyllopoda, order Phyllopoda, and sub-class Entomo- 

 straca. 



