ARTHUR DEWITT WHEDON 421 



A pair of well developed but slender Inferior Longitudinal 

 Tergo-pleural Muscles (plate XXVII, figure 31, tp) is present in 

 all segments from one to seven inclusive. As explained in the de- 

 scription of Calopteryx this muscle seems to have originated by the 

 splitting off of the lower, or inner, part of the Inferior Longitudinal 

 Tergal ^lusclo and the migration of the insertion to a point verj- 

 close to the sternum upon the pleuron. 



Segments two to eight have small Anterior Dorso-ventral 

 IMuscles (plate XXVII, figure 31, adv.) as seen in the Zygoptera. 

 But in addition all the Anisoptera studied possess a second and 

 larger pair in each segment from one to seven: the Posterior 

 Dorso-ventral Muscles (plate XXVII, figure 31 , pdv). These are 

 larger band-like muscles connecting the posterior corners of the 

 tergite with the sides of the sternum near its apex and just in 

 front of the sternellum. No mention of these is to he found in the 

 literature. 



The details of the abdominal muscles in general can best be 

 made out from the figures. 



The sexes differ in the muscles of the segments occupiiMl by the 

 sex organs. 



Second Segment (Plate XXVII, figures 31 and 36). In the 

 males the two pairs of dorso-ventrals are present and especially 

 W(41 developed: the origin of the posterior pair is upon the trans- 

 verse carina near the middle of the segment. As in Calopterijx 

 there are two pairs of Tergo-Sternal Genital Muscles also having 

 their origins upon the carina but just above that of the last 

 named muscle. The muscles of this segment of the females are 

 normal. 



Eighth and Ninth Segments. The eighth segment of males 

 possesses very short and wide but weak sternals, two pairs of 

 lateral tergals, and normal superior tergals. In the ninth seg- 

 ment the sternals of the male are very small (perhaps absent) 

 and lie laterad to the genital pore. A very short, strong muscle, 

 (trs) a Transverse Sternal connects transversely the internal 

 processes of the valves that close the genital pore, and lies be- 

 tween the anterior ends of the sternals. The ninth segment 



TKANS. AM. ENT. SOC, XLIV. 

 4 



