2o6 ARACHNOIDEA, 



CASE more nearly to the Acari properly so called ; doubtless Gamasus 

 marinus, or one of its allies above mentioned. 



The next author who noticed them was Mr. Gosse (Ann. and 

 Mag. Nat Hist 1855), who described three species, and subse- 

 quently Mr. Hodge (Trans, of Tyneside Naturalists' Field Club, 

 iv. and v.) and Mr. G. S. Brady (Proc. Zool. Soc. 1875) have each 

 added one to our list, so that in all we know five species. Both 

 Mr. Hodge and Mr. Brady describe more, but Mr. Hodge's other 

 species seem to be larval forms or varieties of one or other of the 

 known species, and Mr. Brady's come in . elsewhere. We speak 

 here only of those we include in this section. We have been 

 induced to make a separate family for them partly on account of 

 the peculiarity of their habitat, and partly on that of their structure, 

 which, notwithstanding that the above authors refer their species to 

 already known terrestrial genera, does not seem to agree with that 

 of any already described family. They refer some of them to the 

 genera Raphignathus and Pachygnathus of the family Trombidiidse, 

 and others to the family of Oribatidae, and undoubtedly they 

 have some points of affinity with both ; but they also differ from 

 both in important characters, and agree among themselves in 

 others that are peculiar. The chief character given by Duges for 

 the Trombidiid^ is the appendiculated (or unguiculated finger 

 s,nd thumb) palpus. In only one of the species referred to it by 

 the above authors is this present, and then only in a very 

 modified degree. Another constant character of the Trom- 

 bidiidae is the soft pliant silky or velvet-like texture of the skin. 

 The marine species, on the contrary, have either a leathery or a 

 hard skin inchning to crustaceous. In the Trombidiidse the legs 

 are all set well under the body, and their origin is not near the 

 outer margin. In all the sea mites they proceed from the 

 margin. In this latter respect the Oribatidae come nearer to 

 these, as also in having a hard outer skin ; but the hard outer 

 skin in the Oribatidae is chitonous like the covering of a beetle, 

 while in the marine mites it is liker that of a crustacean. But 



