NO. 10 MORPHOLOGY OF GNATIIOTRICHUS — SCHEDL 39 



hranch three other sutures or ridges. Anteriorly there is a short 

 suture dividing the parai)terum from the wing process ; posterio- 

 dorsally another ridge separates the postepimeron (Pepm) from the 

 rest of the epimeron. Ventrally another ridge indicates that part 

 of the episternum which is covered by the sternum and the metacoxa. 



Epistcrnuin. — The episternum is an externally continuous plate 

 having the sha^^e of a narrow triangle with the base facing forward. 

 Ventro-anteriorly it is produced into a hooklike angle, the sternal 

 hook (ci) or anterior sternal hook of Hopkins. The sternal hook 

 fits into an emargination of the sternum, the clavicula (fig. 18, d). 

 Dorsally the extreme angle of the episternum with the pleural suture 

 (probably also containing elements of the epimeron) is produced 

 into the parapterum (e), or coracoid process, and the wing process, 

 or clavicular process (d). From the underside of the parapterum 

 originates a well-developed pronator, or muscle di.sk (fig. 17, tj). The 

 episternum is heavily chitinized and covered by numerous large punc- 

 tures which are interlaced by a network of fine ridges. See also fig- 

 ure 17, h]. When the elytra are kept in the closed position the meta- 

 pleura are nearly completely hidden by them. 



Epimeron. — Between the pleural suture and the lateral margin of 

 the metanotum a more flexible, partly membranous sclerite is in- 

 serted. Posteriorly it is subdivided by a branch of the pleural suture 

 separating the iX)stepimeron from the epimeron proper. While the 

 epimeron proper is more membranous and flexible, the postepimeron 

 is more heavily chitinized. The postepimeron bears dorso-posteriorly 

 a recurved hook, the postepimeral hook (ji), which articulates with 

 the clavicula of the sternum of the first abdominal segments. The 

 hypopleurite (Hpp) extends forward up to a shallow emargination on 

 the dorsal margin of the postepimeron. The anterior margin of the 

 hypopleurite is double reflexed, fitting in a reflexed ridge of the inner 

 layer of the elytra. The area between the anterior margin of the 

 hypopleurite and the dorsal nob of the pleural suture is deeply im- 

 pressed. Epipleurite i of the abdomen is situated in front of the 

 hypopleurite closely attached to the scutellum of the postnotum. 



Metasternum.- — The metasternum is represented as a rectangular 

 continuous plate divided by remainders of a median line. It is illus- 

 trated in figure 18. The anterior margin is medially produced into 

 an angle which extends far between the mesocoxae. This angle and 

 the thickened anterior margin may correspond to the presternum of 

 other segments. The anterior lateral angles (a) are modified to re- 

 ceive the sternal hooks of the metaepisternae. Therefore these emar- 

 ginations should be called the anterior claviculae of the metasternum. 

 Posteriorly the sternum is infolded producing a narrow plate, the 



