ACAKINA PYGNOGOXIDA. 495 



Deg., Argas reflexm. Latr., on Pigeons, occasionally on Man. A. perswus 

 Fisch. Notorious for its bite. 



Fam. Gamasidae. Beetle-mites. Cheliccrae chelate. Pedipalpi five-jointed. 

 The legs end with two claws and a sucker. Tracheae are present. Some of 

 them lead a free life and are predacious, some are parasitic on Beetles and on 

 the skin of Birds and Mammals. Gamasus colcoptratorum L., Dermanyssus 

 avium, Bug.. Pteroptios vetpertttionii Herm. 



Fam. Hydrachnidae. Water-mites. Body globular, often brightly -coloured. 

 Chelicerae usually with a claw-like terminal joint. They have swimming legs, 

 and two or four simple eyes. There are trachens. The larvae, when hatched, 

 adhere with their large suctorial cone to aquatic Insects, on the blood of which 

 they live. Hydrachna cruenta, 0. Fr. Mull. Atax Bonzi Clap., in the mantle 

 cavity of the Unios. Limnnckarc's Uoloscriceus Latr. 



Fam. Trombidiidae (fig. 388). Body brightly coloured and covered with 

 hairs ; the pedipalpus has a claw and a lobe-like appendage. Eyes present. 

 Respiration by tracheae. The hexapodous young live as parasites on Insecta 



FIG. 3$,Q.Pygnogonum IMomle, 

 (regne animal) AB, pair of legs 

 used for carrying the eggs. 



FIG. 389. Trombidium holoseri- 

 ceum (after Megnin). 



and Arachnida, sometimes on Mammalia, and on Man, in whom they (asLtptus 

 autumnali*) produce a transitory affection of the skin. Trombidium Jwlose- 

 ricenm L. Erythrains parietimis Hcrm. Tetranyclnts tclearlus L. Spinning 

 mite. 



Fam. Oribatidae. Chelicera3 retractile and chelate. Pedipalpus five-jointed, 

 with toothed biting plate on its basal joint. Ocelli absent. Orilates alatus 

 Herm., under moss. 



Fam. Bdellidae. The cephalic region is elongated to form a proboscis, and 

 is distinct from the rest of the body. The chelicerae are chelate. The pedipalpi 

 are long and thin. The animals creep about on damp ground. Bdclla longi- 

 cornis L. 



PYGNOGONIDA.* 



Milne Edwards and Kroyer placed the Pygnogonida among the 

 Crustacea ; latterly, however, they have been generally placed between 



* A. Dohrn, " Die Pantopoden des Golfes von Neapel und der angrenzenden 

 Meercsabschnitte," Erne Monographic, Leipzig, 1881. 



