534 PROCEEDINGS OF THE NATIONAL MUSEUM. vol.52. 



The coloration, however, is remarkable in the extent of the black 

 markings, which give the species the appearance of morrisoni, except 

 that the antehumeral black stripe is reduced to an oval spot. This 

 form is of interest because the Columbia River foiTQ is pale (the true 

 severus form) and the State of Colorado form is also pale (probably the 

 true severus), while this form {montanus) is intermediate geographi- 

 cally, but very dark. This darker form may be due to the great alti- 

 tude of Yellowstone Park. 



It is possible that a more extensive survey of the Northwest wiD 

 show that severus, montanus, morrisoni and nevadensis are forms of 

 the same species. Some males of both morrisoni and nevadensis have 

 appendages very similar to those of severus and montanus (see figs. 

 177, 180, 188, 194). The resemblance occurs also in the nymphs, as 

 these have three pairs of lateral abdominal hooks in severus, mor- 

 risoni, and nevadensis. The n}Tnphs of montanus are unknown. 



OPHIOGOMPHUS MORRISONI Selys. 



Live colors, male. — Ohve green thorax and chrome-yellow abdomen; 

 markings intense black. (See fig. 170.) 



Face greenish-yellow with a narrow black hne above the labrum 

 and usually another above the nasus. Dorsal surface of frons black 

 on its posterior half; vertex black except an oval spot posterior to 

 the postoceUar ridge; occiput yeUow. Eyes gray, darker above. 



Thorax ohve green with the following intense black markings: 

 Middorsal stripe 2 mm. wide at the bottom and narrower above; 

 antealar ridge and sinus covered by a line 1 mm. broad, which con- 

 nects with a double humeral stripe 2 mm. broad. This humeral stripe 

 has a narrow green stripe running the entire length of its central 

 line; this green stripe 0.5 mm. wide below. A stripe 1 mm. broad 

 borders the mesinfraepistemum above and posteriorly, and connects 

 with a similar stripe on the dorsal half of the metinfra^pistemum. 

 Lower third of first lateral suture black. A stripe 0.5 mm. wide 

 runs from the antealar sinus below the fore wing to the second lateral 

 suture; a stripe on the second lateral suture 0.5 mm. broad. Legs 

 pale greenish gray; the femora with a heavy external (dorsal) stripe 

 the full length, which is less hea\^ or interrupted on the hind femur; 

 tibiae black with an external pale stripe; tarsi black. Costa yellow; 

 pterostigmas brown. 



Abdomen intense chrome yellow above, gi'eenish yellow on sides of 

 segment 1, yellow on sides of segments 2, and 7-10, and white on 

 the sides of segments 3-6. Markings intense black as follows: A 

 band 1.5 nun. w^de on the upper side of segment 1 running caudad 

 and meeting its fellow on the middorsal apex of segment 2 ; a spot on 

 the anterior end of segment 1 and a spot posterior to the auricle; a 

 lateral stripe extending from segments 3-10 which is broken into a 



