544 BRITISH oribatidj:. 



so thoroughly well known that it would not be desir- 

 able to alter it now by going back to any form of 

 dasypus ; the result of this is, that acarologists feel 

 bound to preserve the name of dasi/pus for a species, 

 but it is not certain that all refer to the same species 

 when they speak of dasijpus. 



The genus is certainly the most exceptional in the 

 family, in its external anatomy, and as a necessary 

 consequence in its musculation; the other internal parts 

 do not vary so much from the usual type. The most 

 striking peculiarity of the genus, which differentiates 

 it sharply from all others in the family, is that the 

 cephalothorax, instead of being anchylosed to the abdo- 

 men, or fixed to it in a manner which admits of little, 

 if any, movement, is here attached by a ginglymous 

 joint, which is very frequently made use of; this joint 

 acts perpendicularly and enables the creature to fold 

 the whole cephalothorax downward and backward, so 

 that its under or sternal surface is pressed against 

 the ventral surface of the abdomen, and the dorsal 

 surface of the cephalothorax is the lowest of all. The 

 creature having the power of entirely withdrawing 

 the legs within the carapace becomes a mere chitinous 

 ball when the cephalothorax is thus folded down (PI. 

 L, fig. 3). To enable the cephalothorax thus to adapt 

 itself to the form of the abdomen and to enable the 

 legs to be withdrawn a most important modification is 

 necessary in the cephalothorax itself, and accordingly 

 we find that, instead of the rigid sternal surface gene- 

 rally found, which is pierced by a distinct mouth- 

 opening with articulated labium or maxillary lip, and 

 rigid acetabula for the articulation of the legs, 

 the whole sternal surface is soft, membranous, and 

 flexible, and that the dorsal surface only is covered by 

 a chitinous plate more or less shaped like the bowl of 

 a spoon with the convex side uppermost, and which 

 has a distinct edge formed to fit against the abdomen. 

 This plate I propose to call the " aspis ;" it often has 

 a strong median carina (H. magna, H. anomala). The 



