296 CRUSTACEA. 



the hand is also naked. The front between the inner antennas is 

 small, triangular, and pointed, and this point rather seems to arise 

 from the spine of the interantennary septum, the front bending down 

 somewhat, so as to meet it and coalesce with it ; as seen from below, 

 the under side passes horizontally inward to the space between the 

 antennae. The tarsus is conical and smooth, but very much incurved, 

 and it is naked, except a short tomentose covering at base. 



III. CRUSTACEA CORYSTOIDEA. 



THE Corystoidea resemble the Cancroidea in the character of the 

 mouth and the efferent channel, and are represented in the latter 

 group by the Cancrinae and Platyonychidae. The extension of the 

 outer maxillipeds over the epistome is common to most of the species 

 of these three groups ; but the true Corystoidea are readily distin- 

 guished by the outer antennae, which are more or less elongated and 

 hairy; and with few exceptions they bend inward and forward. 



Part of the species of this group have the transverse, non-rostrate 

 form of the Cancroids, with sometimes the outer maxillipeds fitting 

 neatly to the epistome ; but these pass into others that are elongate, 

 and approximate in many characters to the Hippidea. In attempting 

 to arrange the genera in natural groups, this relation of the species to 

 the higher and lower orders should be observed. We thus distinguish 

 three families : the first, in which the carapax is transverse and non- 

 rostrate, the outer maxillipeds fitted neatly to the anterior margin of 

 the buccal area, the outer antennae short and subpilose ; the second, 

 having the carapax suborbicular and non-rostrate, the outer maxil- 

 lipeds projecting over the epistome, in Corystoid style, the outer an- 

 tennae short and subpilose; the third, having the carapax orbicular 

 or oblong, and rostrate, the outer maxillipeds projecting over the epi- 

 stome, the outer antennae elongated and pilose. These families, and 

 the genera they contain, are as follows : 



