96 CRUSTACEA. 



to be only five, four, or even three-jointed. In general, it is 

 much larger in the females than in the males, being oval in 

 the former and somewhat triangular in the latter. 



The sub-order Brachyura comprises a very great number 

 of species, respecting the classification of which, crustaceo- 

 logists are not yet agreed. Dr. Leach, followed by M. Des- 

 marets, arranged the groups according to the number of 

 pieces of which the abdomen is composed, both in males and 

 females, — a very simple plan, and one of very easy applica- 

 tion, but at the same time one which produces the most ar- 

 tificial results, some species belonging to the same natural 

 genus being removed thereby to different families. M. 

 Latreille, on the contrary, founding his earlier classifications 

 upon the general form of the body and the disposition of 

 the feet, established seven famiUes, namely, the Nageurs 

 (paddle- legged), Arques (arched front), Quadrilateres (four- 

 sided), Orhiculaires (orbicular {ormed), Trianc/ulaires (triangle 

 formed), Cryptopodes (hidden legged), Notopodes (dorsal 

 footed). Subsequently, however, he took into consideration 

 the form of the mouth and some other characters in addition 

 to the preceding, the result wdiereof was the union of the 

 Nageurs and Arques into one family, and the modification 

 of the others. The latter classification appeared the most 

 natural of any hitherto proposed to M. Edwards, who has, 

 however, been induced, from an investigation of the structure 

 of the different groups, further to modify various portions, 

 and to subdivide the Brachyura into only four great families, 

 which he terms OocyrJiynches, Cyclometopes, Catanietopes, 

 and Oxystomes. 



The Oxyrkyncha (or Maiadce, LithodiadiB, and Macropo- 

 diadcE Leach), comprise the various species of crabs known 

 by the name of sea-spiders, or thorn-backed crabs. The 

 less are long;, the shell more or less narrowed in front 



