a genus of insects belonging to the order of aptera, or such as have no wings. The acarus has 8 legs, 2 eyes, one on each side of the head, and two jointed tentaculike feet. See plate I, fig. 4. There are thirty-one species of the acarus. 1. The elephantinus, is about the size of a white lupin seed, has a depressed orbicular livid body, thickset at the edges, with three furrows on each side of the belly, and a black oval trifid spot at the base or end of the body. It is a native of India. 2. The egyptius, is of an oval shape, yellowish colour, and a white edge or margin. It is a native of the East. 3. The reduvius is plain and oval, with an oval spot at the base. It lives on oxen and dogs. 4. The americanus, is reddish and oval, with the scutellum and joints of the feet white. It is a native of America. 5. The sanguifugus. The hinder part of the abdomen is crenated, the scutellum is oval and yellowish, and the beak is trifid. It is a native of America, and sticks so fast on the legs of travellers, sucking their blood, that they can hardly be extracted. 6. The ricinus is globular, and has a round spot at the base; the feelers are clubbed. It inhabits the bodies of dogs and oxen. 7. The cancrioides, with nippers like a crab, and an oval depressed belly. It is found in the shady places of Europe. 8. The scorpioides, with crab-like nippers, a cylindrical belly, and a small pendulous head. It is of a yellowish colour; and its bite is venomous. It is a native of America. 9. The crassipes has the second pair of legs shaped like those of a crab, and is a native of Europe. 10. The passerinus has the third pair of legs remarkably thicker than the rest. It infests several species of sparrows. 11. The motatorius has the first pair of legs very long and nimble, and frequents the woods. 12. The aphidioides has the first pair of feet longest, and two small horns at the hinder part of the belly. It is a native of Europe. 13. The coleopteratus is black, and the sides are a little crustaceous. It is a native of Europe. 14. The telarius is of a greenish yellow colour. It has a small fling or weapon, with which it wounds the leaves of plants, and occasions them to fold backward. They are very frequently to be met with in the autumn, inclosed in the folded leaves of the lime-tree. 15. The firo has lob-like sides; the four hinder feet are longest; the head and thighs are of an iron colour, and the belly is brilly. It inhabits the farinaceous plants of Europe and America. 16. The exulcerans has very long fetacous legs, but the two first are short. It inhabits the scabies. 17. The geniculatus, is black, and the joints of the thighs are globular. 18. The aquaticus has a depressed red belly, and the hinder part of it obtuse. It inhabits the fresh waters of Europe. 19. The holosericeus has the same characters with the former, only it does not live in water. 20. The baccarum, has a red distended belly, and lives on gooseberries, &c. 21. The muscorum, is of a yellowish red colour, and the hinder legs are long and thread-like. It inhabits mosses. 22. The batatas, is of a blood-colour, and a little rough; the fore pair of legs are as long as the body. body. It inhabits the potatoes of Surinam. 23. The gymnopterorum, is reddish, with two scarlet spots on each side. It inhabits bees, &c. 24. The coleopterorum, is reddish, with a white anus. It inhabits the scarabaeus. 25. The rupestris, is yellowish, with a double coloured line on the back. It is a native of Europe. 26. The longicornis, is red, and the feelers are longer than the snout. It is a native of Europe. 27. The littoralis, is of a tawny yellowish colour, and has blood-red legs. It frequents the shores of Europe. 28. The fungorum is of a yellowish colour, and has a globular clammy belly. It inhabits the mushroom. 29. The icaber, is ash-coloured, and depressed; the sides are scurfy. It is a native of Europe. 30. The falcinus, is red, with two yellow lines on the back; it is forked before. It dwells on the willows. 31. The croceus, is yellow, with a reddish spot on each side of the breast.