Nomenclature. As mentioned above, the prosopon and the nymph of the tsutsugamushi have many characteristics which distinguish it from the other trombidia. These are the pale color and small size of the body, delicacy of the skin, the conspicuous constriction between the cephalothoracic region and the abdomen, rudimentary eyes and tracheal openings, absence of tracheal capillaries, etc. The fact that the thumb or the appendage of the palpus does not start from the side of the fourth joint of the latter but from its end, is another charac teristic which does not occur in other trombidia. From the biological point of view two facts should be mentioned; i.e., the adult female does not deposit eggs in heaps, and in contrast to those of other species, the larvaae hatch out all through the year and feed on mammals. From these characteristics running through all the stages of development, we believe that we are justified in claiming a new genus for the tsutsugamushi. We therefore propose to change the scientific name given to this mite by Brumpt in 1910, Trombidium akamushi, and to introduce instead, according to the suggestion of Drs. Goto and Watase, the name Leptotrombidium akamushi. Determinaton of Leptotrombidium akamushi, N. Sp. Prosopon and Nymph. 1. Pale color. 2. Delicacy of the skin. 3. Distinct constriction between the cephalothoracic region and the abdomen. 4. Rudimentary, sessile eyes. 5. Indistinctnes of tracheal openings. 6. Absence of tracheal capillaries. 7. Crista abruptly widened at the end. 8. One palpal claw. Larva. 1. One scutum. 2. Round pinacles. 3. Legs, six joints, not counting the coxa. 4. Haris on the coza: one each on Joints 1, 2, and 3. 5. Hairs on the scutum, including two tactile hairs, seven; one is in the median line. Specific Determination of Leptotrombidium akamushi, N. Sp. (Trombidium akamushi Brumpt, 1910). Prosopon. 1. Small size 2. Three pairs of sucking discs on the external genitalia. 3. Hairs of the body feathered, club-shaped at the end, and the colorless. 4. The appendage of the palpus tapes distinctly towards the end. Nymph. 1. The size of the body is smaller thant that of the prosopon. 2. Two pairs of sucking discs on the external genitalia. There are no other distinct differences in the external morphology between the proposon and the nymph. Larva. 1. The color of the body is orange-red, but becomes paler after sucking on mammals. 2. The hairs of the body average 110 to 120 in number. 3. One pair of double eyes. 4. The sucking tube is visible when feeding on mammals (Hayashi). 5. The salivary gland is relatively large (Kawamura and Komagata). 6. The number and arrangemetn of the hairs on the legs and mouth parts correspond to the description given by Hirst. 7. The larvae are found all through the year. 8. The larva is the carrier of tsutsugamushi disease in man.