THE ACAEINA OE MITES. 



55 



and 7 species have been taken at a depth of over 3,500 feet. They have been found 

 in nearly all seas, and nearly 100 species are now known. The forms along the coasts 

 of North America have not been studied. The principal genera may be tabulated as 

 below: 



1. Rostrum elongate and constricted at base 2 



Rostrum not constricted at base 3 



2. Palpi apparently three-jointed, separate Scaptognathus. 



Palpi four-jointed, connate at base TrouessarteUa. 



3. Rostrum elongate, palpi separated at base 5 



Rostrum very short , triangular 4 



4. Palpi separated at base Rhombognathus. 



Palpi connate at base Simognathus. 



5. Palpi apparently but three-jointed Coloboceras. 



Palpi plainly four-jointed 6 



6. Third joint of palpus nearly as long as fourth Agaue. 



Thu-d joint of palpus much shorter than fourth Halacarus. 



Fig. 100. 



-Halacarus sp. (Author's il- 

 lustration.) 



Fig. 



101.— Scaptognathus sp. (After 

 Trouessart.) 



Most of the known species come from the French coasts of the Atlantic Ocean, several 

 are known from the Antarctic, and one was described from fresh water. Doubtless as 

 they are more collected the family will be of considerable size. Halacarus (fig. 100), 

 the largest genus, contains over 50 species, several of which bear some resemblance to 

 Scutovertex in the Oribatidae. ' Most of them are marked with brown, reddish, or black. 

 Dr. E. Trouessart, of Paris, and Dr. Lohmann, of Berlin, have published very largely 

 upon them and revised the family. Packard described, under the name of Thalass- 

 arachna verrilli, a species of Halacarus from the coast of Maine, found on algae. 

 Mr. Hall has described two species of Copidognathus (a subgenus of Halacarus) from the 

 California coast. 



