No. 39] ODONATA OF CONNECTICUT: GOMPHIDAE I43 



Dorsal ridge absent on caudal abdominal segments ; teeth of palpi 

 short, sometimes blunt, and not equal in length to the terminal 

 fixed hook ; length of segment 9 never more than three-fourths 

 the width at base 7 



5. Palpi each with 6 teeth (PI. v, Fig. 8) villosipes 



Palpi each with 7 teeth (PI. v. Fig. 6) _ 6 



6. Length of segment 10 half that of segment 9 pallidus 



Length of segment 10 more than half segment 9 furcifer 



7. Dorsal prominences only on segment 9 ; teeth of palpi usually less 



than 6 and obliquely truncate 8 



Dorsal prominences on segments 3, 6, 7, or 8 to 9 ; if indistinct on 

 8 and 9 and not present on other segments, then the teeth of 

 labial palpi not obliquely truncate; teeth of palpi usually more 

 than 6 10 



8. Distal margin of mentum between the palpi concave (curving 



proximad) plagiatus 



Distal margin of mentum straight 9 



9. 3 teeth on palpi (PI. v. Fig. 12) notatus 



4 teeth on palpi (PI. v, Fig. 18) scudderi 



5 to 6 teeth on palpi (PI. v, Fig. 17) amnicola 



10. Lateral spines of segment 9 as long or longer than segment 10 . . . 11 

 Lateral spines of segment 9 shorter than segment 10 15 



11. Lateral spines of abdominal segment 9 twice as long as those of 8; 



abdomen more than three times as long as broad 13 



Lateral spines of abdominal segment 9 equal in length to those of 

 8; abdomen about twice as long as broad, never three times ... 12 



12. Lateral spine on the sixth abdominal segment less than half the 



length of the one on the seventh segment abbreviatus 



Lateral spine on the sixth abdominal segment more than half the 

 length of the one on the seventh segment brevis 



13. Terminal fixed hook of palpus not well developed (PL v, Fig. 2) 14 

 Terminal fixed hook of palpus well developed (PI. v, Fig. 13).. 



vastus; crassus 



14. Lateral spines of segment 9 more than twice as long as segment 



ID ; distal margin of the mentum convex (externus) 



Lateral spines of segment 9 less than twice as long as segment 10; 

 distal margin of the mentum straight fraternus 



15. Dorsal prominences on abdominal segments 3 or 4 to 9 16 



Dorsal prominences on abdominal segments 6 or 7 to 9 17 



16. Teeth of labial palpi 6-8 lividus 



Teeth of labial palpi 8-10 descriptus; graslinellus 



17. Length full grown 28-31 mm.; teeth on labial palpi 6-9 spicatus 



Length full grown 19-24 mm. ; teeth on labial palpi 4 exilis 



Adults, Males 



1. Compound eyes i mm. apart at the dorso-mesal angles or less ; 



occipital ridge absent or represented by a line of hairs in some 2 

 Compound eyes more than i mm. apart at the dorso-mesal angles ; 

 occipital ridge present, distinct 4 



2. Superior anal appendages toothed below in lateral profile brevis 



Superior anal appendages not toothed below 3 



3. Superior anal appendages pale ; viewed from above the lateral 



margins are sigmoid (Lanthus) albistylus 



Superior anal appendages black ; viewed from above the lateral 

 margins are not sigmoid (Lanthus) parvulus 



4. Abdomen not over 32 mm. long 5 



Abdomen more than 32 mm. long 7 



5. Ventral margins of the superior anal appendages, seen from the 



side, entire exilis 



