550 BElTISn ORIBATID^. 



calls Hoploplwra (Tritia) decumana; the genital and 

 anal plates are not separate, but each genital plate is 

 continuous with the anal plate on the same side, and just 

 where the divisions between the genital and anal plates 

 would ordinarily be ; the plates on the opposite sides 

 of the body are joined together, first by a short, trans- 

 verse, chitinous bar, and posterior to the bar by a curious 

 series of interlocking hooks (PL LI, fig. 12). Thus the 

 genital and anal plates cannot really open; but, being 

 slightly chitinized, long, and flexible, they are bent 

 outward to admit the passage of the ovipositor, &c. 

 This organ emerges near the anterior end of the plates. 

 Berlese says that there are eight genital plates in his 

 Tritia decumana, he does not explain how this is, 

 except by a diagrammatic outline and the short explana- 

 tion of this drawing, neither of which are clear to me ; 

 he seems to me to have treated the dorsal plates, the 

 lateral plates, &c., all as genital plates. 



The Ventral plate cannot be said to exist as a sepa- 

 rate organ, it is reduced to a mere setting for, or partial 

 border to, the genital and anal plates to which it is 

 anchylosed ; in H. ardua it is not distinguishable from 

 them, and it is usually slightly chitinized and very incon- 

 spicuous ; generally it is not continuous ; in H. magna 

 the above-named projection at the outer posterior 

 angles of the anal plates probably represents the ventral 

 plate, but notwithstanding such vestigial structures 

 the ventral plate may be said to have become merged 

 in the enormously developed genital and anal plates. 



The Respiratory system. — This has been treated of 

 fully in vol. i. I have not found any tracheae what- 

 ever, unless Olaparede be correct in considering the 

 three minute air-sacs inside the pseudo-stigmata to 

 be tracheaD, as to which see vol. i, pp. 173, 175, &c. 



The Caeca of the ventriculus are usually small and 

 almost globular (PI. E, fig. 2). The alimentary canal 

 is otherwise much of the type ordinary in the family. 



The Ovipositor is short and thick, the genital suckers 

 very large, usually two on each side (PI. L, fig. 13). 



