282 BULLETIN OF THE BUREAU OF FISHERIES. 
PENTAGENIA, the Yellow Drakes. 
This is another genus of very large mayflies. These are almost as large as the brown 
drakes but have shorter legs and tails. The prevailing color is yellowish, but there is a 
wide dorsal band of obscure brownish laid upon the body its entire length; the wings are 
only tinged with yellowish along the front border. 
There is, I think, a single species of this genus in the Mississippi River, though 
Walsh described two. I call them all, therefore, by the name he first used, Pentagenia 
vittigera; for Pentagenia quadripunctaia, the form with four dots on the veins of each 
fore wing (figured on Pl. LXXIII herewith), appears to be only a variant. The con- 
spicuousness of these dots is exaggerated in the figure; in a series of specimens some will 
be found in which one can hardly tell whether the dots are present or absent. 
This genus is very insufficiently known. Nothing has been published hitherto con- 
cerning it except bare and incomplete descriptions of the aduit. Mr. Stringham’s brief 
notes, cited in the preceding pages, are the first that deal with habits; and his care in 
collecting subimagos, together with their cast nymphal skins, make it possible to iden- 
tify with certainty the immature stages. The nymph is described below and is figured 
on Plate LXXIV. 
My specimens of Pentagenia are all from the Mississippi River. (It is reported in 
Banks’s Catalogue elsewhere only from Kansas.) The dates of adults range from June 16 
to September 7, with maximum occurrence in late June. Transformation was observed 
by Mr. Stringham at 7.30 p. m. on June 25. Mr. Schradieck’s imagos from Fairport, 
Iowa, bear date of August 16. Dr. A. D. Howard encountered the nymph in the hed of 
Andalusia Chute only once. There is a single nymph sent me besides, bearing the label 
H. McAdams, Keokuk. 
The nymph of Pentagenia is similar to that of Hexagenia but is more yellow and 
more hairy, and a glance at the denticulations of the front of the head is sufficient for 
certain identification. It may be described as follows: 
Length, 24 mm.; tails, 6 mm. additional; antenne, 4 mm. 
Color pale yellowish, deepening to brownish posteriorly on the dorsum, whitish below. The head 
in front, the legs exteriorly, and the lateral lobes of the abdomen are densely clothed with shining, 
golden hairs. Eyes and ocelli black. 
The diffuse brown of the thoracic dorsum becomes a broad definite longitudinal stripe on the 
abdomen, nearly as wide as the segments. On each segment a pair of obliquely placed pale dashes is 
included in the brown. 
Antennz wholly pale and naked. Head with a strongly chitinized, two-toothed, frontal promi- 
nence, and a ridge bearing two unequal denticles above the base of each antenna. Cheeks and outer 
edges of palpi densely clothed with brushes of yellow hair. 
Mandibular tusks very strong, bare and upcurving in their apical third, dilated basally and bearing 
an external carina that is edged with irregular, brown denticles. This portion of the tusk is hairy 
within, and at the base externally. 
Top of head and thorax smooth, shining, save for some short, yellowish pubescence about the wing 
foots. 
Legs short and heavy, hairy on front and rear margins, especially the front legs. Front femora 
flattened and quadrangular, with an expanded inferior lobe beside the knee joint that bears an immense 
brush of stiff, yellow hairs. Front tibia dilated apically and bearing a similar inferior lobe that is 
densely clothed with shorter, stouter bristles; bearing also an external denticulate-margined ridge of 
increasing prominence distally where it ends in a strong and conspicuous brown tooth. Just beyond 
this, at the apex of the tibia, another similar tooth lies against the base of the short cylindric tarsal 
