The insects long known under the name of _Ricini_, and to which many other appellations have been given, deserve to figure in the first rank in this group. They have always perplexed entomologists, who seem to consider them as parasites allied to acaridæ and lice. It has, however, been long known that they have no trunk to suck with, and that they have two small scaly teeth, which rather serve for the purpose of biting. A long time since, the examination of their stomach proved that they contain only morsels of skin instead of blood. This has induced many entomologists to place them in the same order as grasshoppers, that of Orthoptera. Lyonet has given figures of several of those which he studied with the care which he so well knew how to employ in his anatomical investigations; and in 1818 Nitzsch, a professor at Göttingen, had brought together so great a number of them, that it required several days to examine his collection; he began the publication of his catalogue, but has not had time to finish it. Several other entomologists and anatomists have since taken up the subject. We owe the description of several hundred species to Mr. Denny. Mons. F. Rudow has lately made known a great number of species which he has collected from the skins of birds coming from Japan, Australia, 70 Africa, and the two Americas. Professor Grube, of Breslau, has published the description of the insects and acaridæ found during the travels of Middendorf in Siberia. These descriptions relate especially to the Philopteræ of birds, the Pediculinæ of the mammalia, a flea of the _Mustela Siberica_, and an acarus of the _Lemmus_. Quite recently, an American naturalist, Mr. Packard, who has undertaken the study of so many different subjects, has published in the "American Naturalist" the description, accompanied by an engraving, of the _Menopon picicola_, found on the _Picoides Arcticus_ from the lower Geyser basin, Wyoming territory, also of the _Goniodes Merriamanus_, the _Tetrao Richardsoni_, and the _Goniodes mephitidis_, found on a _Mephitis_ from Fire-Hole Basin, Wyoming territory; of the _Nirmus buteonivorus_, from a _Buteo Swainsonii_; and of _Docophorus Syrnii_, from _Syrnium nebulosum_. A great number of these insects live between the feathers of birds, and can be more easily observed, since they detach themselves after the death of their host. They are easily found on the skins of birds prepared for museums. These ticks form a family under the name of _Riciniæ_, and this family is divided into two parts, the _Liotheidæ_ and the _Philopteridæ_.