124 ZOOLOGY. 



United States upon various Coleoptera, particularly those which live in 

 dung. Five species are described by Say. 



The genus Argas {A. fisclieri^ pi. 77, fig. 46; A. savinii, fig. 47) is 

 remarkable for containing the poisonous A. jpersicus., which lives in old 

 houses about Miana in Persia, and is said occasionally to cause the death 

 of foreigners, although it is not fatal to the natives. 



A species has been described by Guerin, which was discovered in Central 

 America by Salle, who states that he and his comj)anion were awakened 

 from profound sleep by sharp bitings or stingings, and upon getting a light 

 he found his hands covered with blood, and swellings like large fleabites. 

 His com2:)anion supposed that they had been stung by wasps, but upon 

 awaking the muleteer, it was found that they had been attacked by an 

 insect called talaje.^ and upon searching, some of the Argas were found 

 swelled with blood, and others empty, with the skin rugose. They live in 

 the crevices of the walls in old houses, coming out at night and returning 

 before morning. 



Fam. 6. Hydrachnidxß. This family includes the small globular and 

 oval forms found in water, in which the coxai are so broad as to form a 

 kind of sternum. The young of Ilydrachna are born with'six feet. They 

 swim about for some time, and then affix themselves to the bodies of aquatic 

 insects by the anterior extremity, when the palpi and feet seem gradually 

 to be withdrawn, and the exterior of the body becomes a kind of sac or 

 cocoon, but the rostrum still jienetrates the smaller extremity to draw 

 nourishment from the insect to which they are affixed. The young animal 

 leaves this skin by moulting, and attaches itself to a plant, where another 

 moult takes place before it resembles the adult. During the period of 

 attachment to aquatic insects, these animals can be transported by flight, 

 and distributed to the various small detached ponds in which they are 

 found. 



The genus Unionicola., Hald., 1842, differs from Hydrachna in being 

 unable to swim, in having the palpi conical, the antepenultimate articulation 

 the longest and very thick, and the point simple, whilst in Hydrachna, as 

 represented by Duges, these organs are cylindrical, with a double terminal 

 claw ; the penultimate articulation is the largest, and the nails of the feet 

 are not bifid as in Unionicola. This genus is parasitic between the folds 

 of the mantle in the Unionidm. H. trimigularis., Say {avif&rmis^ Hald.), 

 inhabits Unio cariosus ; it is black, and has a Y-shaped white mark upon 

 the back. IT. reticulatus^ Hald., is pale, ochraceous, and infests TJnio mridis. 

 The last is a large species, being a line and a half long, the length in 

 general hardly reaching a line. From their mode of life, it is probable that 

 in this genus the system is oxygenated through the skin from the water. 



Farn. 7. Tromhidiid(ß. This family is composed of the larger land forms, 

 which bear some resemblance to the PhalaiigiidcB in the next order. The genus 

 Tromhidium is usually of a bright red, which extends over the feet and palpi, 

 and the surface is velvety, which characteristics, together with their slow 

 motions, will render them recognisable in the forests. The body is com- 

 posed of two portions, the trunk, and an anterior and inferior portion, 

 328 



