124 ZOOLOGY. 
United States upon various Coleoptera, particularly those which live in 
dung. Five species are described by Say. 
The genus Argas (A. fischeri, pl. 77, fig. 46; A. savinii, fig. 47) is 
remarkable for containing the poisonous A. persicus, 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 Guérin, which was discovered in Central 
America by Sallé, who states that he and his companion were awakened 
trom 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 companion 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 ¢alaje, 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. Hydrachnide. This family includes the small globular and 
oval forms found in water, in which the coxe are so broad as to form a 
kind of sternum. The young of Hydrachna 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to be withdrawn, and the exterior of the body becomes a kind of sae or 
cocoon, but the rostrum still penetrates 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 Dugés, 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 Unionide. HH. triangularis, Say (oviformes, Hald.), 
inhabits Unio cariosus; it is black, and has a Y-shaped white mark upon 
theback. UW. reticulatus, Uald., is pale, ochraceous, and infests Unzo viridis. 
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. 
Fam. 7. Trombidiide. This family is composed of the larger land forms, 
which bear someresemblance to the Phalangiidwin the next order. The genus 
Trombidium 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 
