ART. 12. NAIADS OF THE GENUS HELOCORDULIA KENNEDY. 6 



The identity of this HelocorduUa exuvium is fairly certain, first, 

 because of the circumstances under which it was found; second, be- 

 cause it is nearly identical with Needham's description ^ of the naiad 

 of uhleri and with specimens of the latter sent the writer by Doctor 

 Walker ; third, it differs in the same characters from the known Soma- 

 tochlora naiads {elongata,^ tenehrosa, and semicircularis) as does 

 uhleri. The HelocorduUa naiads have the lateral spines on abdominal 

 segment 9 approximately as long as the dorsum of the same segment, 

 while in the three Somatochloras they are distinctly less. 



The following description of the naiad of selysii has been drawn 

 to parallel that of uhleri by Needham.^ The latter species has been 

 so well described that it is needless to redescribe it here. Figures of 

 the uhlen naiad are given for comparison with, those of selysi. The 

 exuvium of selysii as well as two of uhleri have been deposited in the 

 United States National Museum. 



DESCRIPTION OF THE NAIAD OF HELOCORDULIA SELYSII (Hagen). 



Color completely obscured by a thin but complete incrustation of 

 mud. Total length, 20 mm. ; abdomen, 12 mm. ; hind femur, 6.5 mm. 

 Width of head 5.5 mm. and of abdomen 7 mm. (See pi. 1, figs. 6-12.) 



Head nearly twice as wide as long. Eyes small and not prominent, 

 their front contour continuous with the front contour of the head. 

 Frons broadly angulate anteriorly, occiput slightly incurved, the 

 sides of the head sloping rapidly entad to the occipital angles. Each 

 occipital prominence with a lateral and a dorsal row of long spine- 

 like hairs. 



Antennae with segments about equal in length, segments 1 and 2 

 being heavy while 3-7 are slender. (See fig. 11.) 



Labium reaching caudad to between the bases of the middle legs, 

 the sternal sulcus which houses the base of the labium being fringed 

 behind by a sinuate row of long hairs between the middle coxae. 

 Labium as broad as long with the middle lobe a right angle and its 

 edges minutely crenulate and armed with numerous short spines. 

 (See figs. 7 and 8.) The mental setae 13-14 in number, of which 

 the outer 8 are very long, while the inner 5-6 are minute. The 

 lateral setae are 7 in number and have parallel to their bases a row 

 of short stiff spines along the dorsal edge of the lateral lobe. Mova- 

 ble hook slender and 2-3 times as long as the depth of its insertion. 

 8-9 crenulate teeth on the lateral lobe, each tooth with a gi-aduated 

 series of 3-5 long, slender, sharp spines, the longest of these in each 

 series being half the length of the movable hook. 



8 Needham, Aquatic Insects in the Adirondaclcs, New York State Museum, Bull. 47, p. 497, 

 1901. 



'' Needham's description (N. Y. State Mas., Bull. 47, p. 500) may not be elongata as the 

 individual described doea not appear from the text to have been reared. 



8 See footnote 6. 



20183— 25— Proc.N.M.vol.64 15 



