ARTHUR DEWITT WIIEDOX 379 



Each segment is composed of the usual sclerites. 'Ilie tergite 

 is very bi'oad and covers the dorsal, lateral, and even part of the 

 .v(Mitral aspects of the abdomen. It is heavily chitinized and 

 further strengthened by thick ridges or lines, carinae, about the 

 margins and even through its interior. In Anisoptera the fol- 

 lowing are present: (Ij the anterior transverse carina boi-dering 

 the anterior suture, (2) the posterior transverse carina bordering 

 the posterior suture, (3) the ventral carinae following the pleural 

 margins of the tergite, (4) the mid-dorsal carina along the median 

 line, (5) the lateral carinae forming the lateral angles of the body, 

 and (6) supplementary transverse carinae usually found in the more 

 anterioi' dorsal portions of the terga of the basal segments of the 

 larger forms. The posterior, transverse, lateral, mid-dorsal, and 

 supplementary transverse carinae may be more or less denticu- 

 late. Their importance will be clear when the muscle attach- 

 ments are described. The Zygoptera usually lack the lateral 

 and supplementary transverse carinae, but are in other respects 

 as stated above. 



The pleura are narrow, non-chitiniz(Hl bands between the 

 terga and the sterna. They bear the spiracles only, except the 

 ninth and tenth, these lying toward the anterior end and just 

 back of the second lateral processes of the sternum. Consid- 

 erable difficulty is experienced in most species in drawing the 

 overlapping tergum back from the sternum far enough to give a 

 clear view of the pleura. 



The sternite is an elongated, narrow, slightly ventrally convex 

 plate which narrows backward and ends in a pointed, highly 

 chitinized process or sternellum, this overlapping the anterior 

 broadly rounded end of the succeeding sternite which in turn 

 extends a little forward of the anterior transverse carina of its 

 segment. An anterior and a posterior pair of sternal processes 

 (apodemes), rib-like chitinous rods, lie at and back of the inter- 

 segmental suture. These and the point of union between ster- 

 num and sternellum are regions of muscle attachment. In 

 Zygoptera the sternum is almost completely concealed by the 

 approximated edges of the tergum. In all forms, however, the 

 sterna of the basal three segments are visible: in the female as 

 plates, in the males with modifications due to the copulative 

 organs. 



TRANS. AM. KNT. SOC, XLIV. 



