THE ACABIXA OR .VITES— BANKS. 



41 



frequently in shallow water, but some have l)een dredged at consider- 

 ah\e depths. The adults are free^ and feed on diatoms and other 

 minute vegetation. The young of some forms feed on the eggs of 

 Copeopods, while others are attached to various animals. One is 

 known to occur on a (7iito/t. They are from one to two millimeters 

 in length, and their colors depend largely on the nature of their food. 

 The young have the general appearance of the adults, and nymphs 

 sometimes possess rudimentar}- genital organs. The legs o'f the 

 nymphs have each one less joint than in the adults. They have Ix^en 



Fi<;. 69.— Halacaeus sp. Fig. 70.— Scaptognathus sp. (after 



Trouessart). 



found in nearh' all seas, and about seventy species are now known. 

 The forms along the coasts of North America have not been studied. 

 The principal genera ma^" l)e tabulated, as below. 



1. RoBtruni elongate and constricted at base 2. 



Rostrum not constricted at base 3. 



2. Palpi apparently three-jointed, separate - Scaptognathus. 



Pal{)i, four-jointed, connate at base TrovessarteUa. 



3. Rostrum elongate, palpi separated at base 5. 



Rostrum very short, triangular 4. 



4. Pal j)i separated at base RhomliogjuitJi iix. 



Paljii connate at base SimogiiutJnts. 



5. Palpi ajiparently but three-jointed Colohoceras. 



Pali>i plainly four-jointed 6. 



6. Third joint of palpus nearly as long as f< >urth .' Agaue. 



Third joint of palpus much shorter than fourth Halacurns. 



