34 ARKIV FÖR ZOOLOGI. BAND 2. N:0 8. 



allied to each other that such splitting up would be obnoxious. 

 The genus Artacarus must therefore be cancelled, and its single 

 species named by Cook, viz. A. liheriensis, must even be 

 considered quite unrecognisable until a real description with 

 good figures bas been published. 



Two genera remain, viz. Schizomus and Trithyreus. The 

 difference between them is that in Schizomus the surface of 

 the second thoracic tergite is reticulated without any median 

 suture or membranoas strip (but sometimes with a whitish 

 hne beneath the skin), while in Trithyreus it shows either a 

 median suture or a less or more membranous strip; in order 

 to observe the quality of the surface with certainty it must, as 

 a rule, be examined dry with a strong lens. It may be added 

 that in all (five) species of Schizomus Avith the abdominal 

 flagellum well preserved this flagellum is four-jointed, while 

 it is three-jointed in all species of Trithyreus, but I am not 

 sure that in species unknown to me this very small difference 

 always accompanies that in the second thoracic tergite. The 

 forms which must be referred to Schizomus do not show any 

 further character not met with in some species of Trithyreus, 

 and vice versa; the difference in the structure of the second 

 thoracic tergite must be considered rather unimportant, and 

 for these reasons the value of the genus Trithyreus is slight, 

 but it may be maintained as a subgenus. 



Spccific Cliaracters. — Adult males are very easy to se- 

 parate; among their specific cliaracters those shown by the 

 abdominal f lägel lum are excellent, but sometimes also the last 

 abdominal segment or the palps present good marks of di- 

 stinction not met with in the other sex. Adult females of 

 different species are on the whole considerably more similar 

 and therefore more difficult to describe and figure so that 

 they can be recognized with certainty not only from the other 

 species known but from undescribed forms. Adult females 

 differ more from each other than immature specimens of the 

 same forms, but I have unfortunately not been able to discover 

 any good character between adult and immature female spe- 

 cimens; size and especially colour is generally important for 

 such discrimination, but a trenchant character between females 

 of small species and immature specimens is wanting. Of eight 

 species I have seen adult males; judging from the labels seven 



