14 ARKIV FÖR ZOOLOGI. BAND 2. N:0 8. 



tactile hairs on the other pairs — are mentioned below in 

 the paragraph dealing with the organs of sense. 



Abdomen (Pl. ]., figs. la — le and 1 p). — In all Uro- 

 pygi abdomen consists of twelwe free and well developed 

 segments and terminates in a »flagellum». In each of the 

 nine anterior segments broad connective skin is found late- 

 rally between tergite and sternite, while the three posterior 

 segments are entire, ring-shaped. First tergite (fig. 1 b, i) 

 is well chitinized; the first sternite (fig. le, 1) is separated 

 from the posterior thoracic sternum by a strip of thinner 

 skin which is shorter than a similar skin between the first 

 and the second sternite; the first sternite is in Oxopoei as 

 firmly chitinized as the second, while in Tartarides it is less 

 firmly but yet conspicuously chitinized as a narrow (short) 

 transverse band on the anterior part of the abdominal stalk 

 which is formed by the first segment. In both tribes the 

 second sternite is a very long plate. In Tartarides (Pl. 1., 

 figs. 1 c and 1 p) the third sternite is very short, several 

 times shorter than the fourth at least at its lateral margin, 

 which is nearly as long as that of the fifth; in Oxopoei both 

 the third and the fourth sternite is short, each much shorter 

 than the fifth. (A conspicuous sexual difference in the shape 

 of second to fourth sternite in the Tartarides is mentioned 

 below.) In Oxopoei a pair of conspicuous muscular impres- 

 sions are found on second to eighth tergite and on fifth to 

 eighth sternite; among the Tartarides similar muscular im- 

 pressions are well developed in two of the largest species, 

 Trithyreus Grassii Thor. and T. suhoculatus Poc, on the 

 third to seventh tergite and the fourth to seventh sternite, 

 while in a smaller species as Schizoynus Simonis n. sp. these 

 impressions are faint or at least some of them ha ve comple- 

 tely vanished. Tenth to twelfth segments are rather similar 

 in both tribes, but the remarkable yellowish »spöts» generally 

 existing in Oxopoei on the sides of the twelfth segment are 

 always absent in Tartarides. Furthermore, in many Tarta- 

 rides the last three segments, and especially the twelfth, 

 are somewhat or even much thicker in the male than in the 

 female. In Trithyreus p^ocerus n. sp. the twelfth segment is 

 nearly twice as deep in the male (Pl. 5., fig. 3 i) as in the 

 female (Pl. 6., fig. Ib), its upper half is produced backwards 



