540 PROCEEDINGS OF THE NATIONAL MUSEUM. 



indented near the base of the appendage. Each branch terminates 

 in a short, heavy, black spine directed dorsad. (See figs. 200, 201 .) 



Anterior hamules spatulate, spoon shaped with a long ventral hook 

 (see fig. 199). One male shows a small spme on the tip of this hook. 

 This apical spine is an individual character, some individuals of other 

 species showing it. Posterior hamules terminating in a straight tlim 

 limb with subparallel sides and a square tip. The hamules are similar 

 to those of hison and severus, from either of which the male can be 

 distinguished by the terminal appendages. 



The female is distinguished by having two very short, heavy, widely 

 spaced spines on posterior edge of occiput (fig. 203) and a deep semi- 

 circular depression on its superior surface. Probably this depression, 

 which is peculiar to the female of this species, is to adjust the occiput 

 to the extremely short inferior appendage of the male. (Vulva, fig. 202.) 



OPHIOGOMPHUS BISON Selys. 



Live colors, male. — Thorax rich green; abdomen yellow with 

 black markings. (See fig. 164.) 



Face pale greenish yellow; eyes gray; vertex entirely black, this 

 color extending onto the posterior edge of the frons; occiput yellow. 



Thorax a rich bright green with the following dark brown mark- 

 mgs: A middorsal stripe 1 mm. wide connecting along the antealar 

 ridge with a broad (1.5 mm.) usually solid humeral stripe. (In some 

 specunens the hiuneral stripe has a very narrow internal green line.) 

 The latero-alar ridge brown caudad to the second lateral suture, which 

 is narrowly brown. The mesmfraepisternum and metinfraepisternima 

 as well as the prothorax heavily mottled with black and usually 

 pruLQOse. Femora with a heavy external (dorsal) black stripe; 

 tibiae and feet black. Costa edged with yellow. Wings heavUy 

 veined and with a slight flavesence. Pterostigmas black. 



Abdomen bright yellow above the black lateral markings and white 

 below. The black markings are as follows: A broad stripe extendmg 

 along the upper side of segments 1 and 2, and converging to the dorsal 

 apex of segment 2; a narrower lateral stripe (1 mm. wide) extending 

 along sides of segments 2-10 (pale brown on 9 and 10). This stripe 

 has a rectangular enlargement at the apical end of each segment. 

 These enlargements do not coalesce with their fellows of the opposite 

 side on the middorsal Ime except at the extreme apex of each seg- 

 ment, and on segments 9 and 10 they are widely open on the middorsal 

 Ime at the apex. Segments 3-8 with a spot m the postero-ventral 

 angle. (For structural details, see figs. 165-167.) 



Female. — Colored hke the male but the postocellar region of the 

 vertex yellow. Femora usually with only the outer half in the first 

 pair and the outer fourth in the others black; tibiae with an external 

 pale stripe. Segment 9 of the abdomen less heavily marked than in 

 the male, and segment 10 yellow. (Structural details, figs. 168-169.) 



