METAZOA CRUSTACEA. 351 



having become consolidated without leaving a trace of the 

 sutures, in this way a wedge-shaped implement is pro- 

 duced which is an efficient organ in burrowing. It is also 

 aided in the work by the short, stout cephalothoracic legs. 

 Thus equipped, the creature burrows backward into its 

 hole with great rapidity and is wholly hidden save the tips 

 of its small antennae. 1 



Although the adult Hippa is more of a burrower than 

 a swimmer, nevertheless when undisturbed it will leave 

 its burrow and swim about by means of its thoracic and 

 abdominal feet. The antennae of Hippa are unique 

 organs. When extended they curve like the horns of a 

 deer and are provided with long hairs on the outer side. 

 These are seen in No. 858, but more plainly in PI. 859, 

 where they are extended. When living, the animal usu- 

 ally carries them folded about the mouth, and, according 

 to Smith, one of the principal offices of these organs is to 

 keep the anterior appendages mouth parts, etc. free 

 from all foreign substances. 



A relative of Hippa is found in Raninoides levis M. 

 Edw. (No. 860). Here the entire carapace has many 

 irregular serrated markings. The front edge is provided 

 with slender pointed teeth and the rostrum is composed 

 of two parts and appears to be movable. The front of 

 the cephalothorax is hairy. The last pair of legs are 

 reduced in size and pushed up on the back. The arms 

 have become flattened and twisted, till the movable jaw 

 of the claw is inside instead of outside or above. 



One of the most remarkable and interesting modifica- 

 tions of structure is found in Dromia vulgaris M. Edw. 

 (No. 861), which lives with the sponge or sometimes in 

 coral. The external skeleton has become soft and horny 



1 Smith, Trans. Conn. Acad. Arts Sci., Ill, 1876, pp. 311, 313. 

 According to Verrill (Rep. U. S. Comm. Fish and Fisheries, I, 

 i87i-'72, pp. 338, 339) Hippa talpoida burroyrs like a mole, head 

 first, instead of backward. 



