GENUS hoplopiioi;a. 545 



next peculiarity is in the ventral plate ; it will be seen 

 by the description at p. 550, that the ventral plate 

 proper can hardly be said to exist but is merged in 

 the very large genital and anal plates ; but referring 

 to the whole of these structures as the ventral plate 

 for the purpose of understanding their joint movement 

 as one plate, we notice that instead of being anchylosed 

 or firmly and almost immovably fixed to the dorsal, 

 as a ventral plate usually is, they are only attached to 

 it by a flexible membrane and are capable of free 

 motion. The mode in which this power is employed is 

 as follows : when the creature, having been closed up, 

 wishes to extend itself and put out its legs the ventral 

 plate is drawn by its levator muscles upwards so as to 

 be nearer to the dorsal surface ; the anterior part of 

 the plate is drawn furthest up. This motion leaves 

 less space within the body, and doubtless assists in 

 forcing the legs out ; they emerge in front of the con- 

 cave edge of the ventral plate (PI. L, figs. 2, 8). When 

 the creature closes up again the ventral plate is drawn 

 downward against the sufflexed edge of the notogastral 

 plate, and the legs are drawn upward into the space 

 so left. Another pecuHarity is in the number of joints 

 in the palpi, which will be dealt with at length under 

 the head " palpi." 



Berlese proposed making a separate genus (" Tritia'^) 

 for the species which have tridactyle claws, and the 

 peculiar genital and anal plates of H. ardua (' Acari, 

 &c. Ital.,' fasc. vi) ; he has subsequently abandoned 

 this idea (ibid.. Notes, fasc. iii) ; but Oanestrini still 

 retains it (' Prospetto dell' Acarofauna Ital.'), and Ber- 

 lese himself continues to use the name. 



The Rostrum cannot be said to exist as a distinct 

 part, and all distinctions of frons, gense, provertex, and 

 dorso-vertex are entirely lost ; but the rostral hairs 

 persist, and are usually rather large, and placed high 

 up on the curve of the aspis. 



The Labium is not as hard and chitinous, nor as dis- 

 tinctly articulated an organ, as is usual in the Oriba- 



VOL. IT. 35 



