28 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 94 



separates the epimeron into two parts, the notepimeron (nepm) and 

 the sternepimeron (sepm). The sternepimeron Hes along the epi- 

 sternum, separated from it by the pleural suture (fis), and is slightly 

 longer and considerably wider than it. Its posterior part overlaps the 

 lateral end of the first abdominal tergite and the spiracle of that seg- 

 ment, as well as the tip of the postnotum of the metathorax and, 

 anteriorly, the caudal end of the epimeron of the mesothorax. Its 

 cephalic end is the pleural wing process (pzvp) but apparently is not 

 specially modified. Its surface is rather convex and marked with a 

 distinct impressed line (sepl) which sets off the anterior quarter and a 

 narrow band along the dorsal edge. The surface is clothed with setae 

 similarly to the episternum except for a space dorsad and caudad of 

 the sternepimeral line. The anterior part bears only a few small 

 scattered setae. The notepimeron (nepm) is united to the sternepim- 

 eron at its cephalic end, at which point the former is a narrow band. 

 It expands posteriorly into a flat oval plate, bearing a few small setae 

 anteriorly and a few minute sensory pores on the sides of the disk, 

 and its surface is rather strongly strigulose (fig. 4 D). 



The metathoracic spiracle (figs. 3 A, sp. Ill, 4 E) lies in the mem- 

 brane anterior to the epimeron and along the dorsal side of the meso- 

 thoracic pleuron. It is very pale and membranous, without sculpture 

 or vestiture, and is not surrounded by a definite sclerite. It is entirely 

 unlike the spiracles of the mesothorax and abdomen as it has no sieve 

 apparatus, being composed of two sclerotic lips which fold together 

 to close the opening. It is longer and much more slender than the 

 other spiracles and is difficult to differentiate from the surrounding 

 membrane. 



THE ENDOTHORAX 



The endoskeleton of the thorax is known collectively as the endo- 

 thorax. It is composed of invaginations of the tergal, pleural, and 

 sternal regions of each segment, and these apodemes are termed the 

 endotergites, the endopleurites, and the endosternites respectively. The 

 sclerotized tendons and some small invaginations are part of the endo- 

 skeleton but are not considered here. 



The endotergites (fig. 5 A) are found typically only in the meso- 

 thorax and metathorax. In the prothorax the endotergites are repre- 

 sented only by a rather indefinite group of processes on the hypomera 

 in the region of the coxal cavity and the trochantin. These bear a 

 large muscle disk (fig. 5 A). In the mesothorax the anterior margin 

 of the prescutum is deflexed to form a transverse ridge — the ante- 

 costal ridge or prephragma (prph), which bears a pair of large muscle 



