839 



Ps.O.s. 



the sittings on a Hat dish suspended over a large funnel, and 

 placing the funnel and all in the sunlight. The sunlight drives 

 the mites out of the sittings, and they fall through the funnel 

 into a vial below. 



The most convenient and satisfactory mounting media for 

 oribatids are Canada balsam and dammar balsam. Dissections 

 of the mouth-parts are frequently necessary. Material must 

 often be rendered partially transparent by means of potassic 

 hydrate or eau de Labrraque. 



In making the drawings I used an Abbe camera lucida. 

 The measurements were made with an ocular micrometer. 



External Anatomy. 



The body in the Oribatoidea (Fig. 1) consists of an anterior 



narrower region termed the 

 cephalothorax, and a posterior, 

 much larger, portion termed 

 the abdomen. The union of 

 these two regions is more in- 

 timate in some genera than in 

 others. There is usually an 

 evident division between the 

 cephalothorax and the ab- 

 domen except in the genera 

 Scutovertex and Aincnis. In 

 two genera, Hoploderma and 

 Phthiracarus, t h e cephalo- 

 Fig. l. Damseus nitens, dorsal view. thorax is hinged to the ab- 

 domen in such a way that the former can be folded down 



against the ventral surface of the latter. 

 The cephalothorax may be divided into 



two parts; the rostrum (Fig. 1, Ro.) and 



the posterior portion. The rostrum is the \ 



anterior hood-like portion which protects 



the mouth-parts. Upon the rostrum is 



found a pair of stout hairs termed rostral 



hairs (Fig. 1, Ro. h.); sometimes the 



Tctp. — 



.Mr. a. 



lsf seg. 



Fig 



Oribata banksi, man- 

 dible. 



