Since Baker and Wharton (1952) regarded the genus Mealia Trouessart, 1897, as a synonym of the genus Dermatophagoides Bogdanoff, 1864, many authors (Sasa, Dubinin, Baker et al., Hughes, Fain and others) have adopted the genus Dermatophagoides for the free-living mites which abound in the house-dust and other sources. When Fain (1966) redescribed Dermatophagoides pteronyssinus (Trt.) which was a dominant species in the house-dust, he suggested that it was impossible to define with certainty that D. pteronyssinus (Trt.) is not a synonym of D. schermetewskyi Bogdanoff, 1864. He did not, however, regard the former as a synonym of the latter, and stated that "Nous proposons donc de maintenir les deux especes et d'attendre que la decourverts de nouveau materiel puisse nous fixer sur le statut de D. scheremetewskyi". When he completed a monograph (1967a) on the genus Dermatophagoides, he could not include the redescription of the type species of the genus, i. e., D. scheremetewskyi. This means that the genus Dermatophagoides was reestablished without defining type species. That the dominant form found in the housedust is identical with Trouessart's Mealia pteronyssina seems highly probable on the following grounds : 1) Dr. Fain ascertained that his materials (D. pteronyssinus) was identical with the type series of M. pteronyssinus which was actually preserved in Berlese Collection of Florence with data written by Trouessart (1901) "Habitat : Sur des peaux de Mammiferes preparees et attaquees par des Insectes rongeurs (par M. Petit aine, de Paris", 2) we ascertained the identity between our materials from the house-dust and D. ptronyssinus sensu Fain, and found that our material falls within the category of the genus Mealia Trt., and specifically coincide with M. pteronyssina Trt. according to the original description. In Bogdanoff's original description of D. scheremetewskyi, we found that D. scheremetewskyi is definitely distinguishable morphologically from the species of the genus Mealia Trt. In the female of Bogdanoff's D. scheremetewskyi, 1) palpal tarsus is rather slender and pointed forwards, 2) a pair of external vertical setae are present and are provided with some ten pectinations, 3) a pair of pores which may be traces of internal vertical setae (which must have fallen off) are present, but are drawn by mistake between epimera I and II of ventral view (1B), 4) the propodosmal shield is lacking but that part is carefully and finely striated, 5) both posterior ends of epigynium (lesextremites de l'arc superieur) turned slightly outwards and reached the same level of the scapula of trochanter III, 6) the posterior ends of lateral vulva (les extremites posterieures de ce second arc) reached the same level of the scapula of trochanter IV. In the female of Mealia pteronyssina Trt., 1) palpal tarsus is rather short and turned strongly inwards, 2) both external and internal vertical setae absent, 3) a distinct propodosomal shield is present, 4) the epigynium is likely crescent or house-shoe shaped and the posterior ends do not reach the level of the scapula of trochanter III but may or may not reach the level of the anterior ends of epimera III, 5) the posterior ends of lateral vulva exceed beyond the level of the scapula of trochanter IV. Thus, it is clear that Bogdanoff's genus Dermatophagoides differs from the genus Mealia Trt. We propose, therefore, that the genus Mealia Trt. should be revived for the forms of free-living mites in the house-dust instead of the genus Dermatophagoides, which should be maintained for the true exoparasitic forms as like as the original habitat. It was also emphasized in the present paper that the male mite (described in the Bogdanoff's paper at the same time with the female of D. scheremetewskyi) is not concerned in the problem of the identity of D. scheremetewskyi Bogd., because he only sta

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