132 EEV. A. E. EATON ON EECENT EPHEMEEID.E OR MAYFLIES. 



sparingly tul)erculated at the sides, and posteriorly near the middle. Mesonotum with 

 a pair of small tubercles on the praescutum, anotlier tubercle at each of the lateral angles 

 of the scutum, and a single tvibercle on the scutellum. The dorsal spines on segments 3-9 

 are slender and somewhat unciform, with their points directed posteriorly. Length of 

 body 14 ; outer sette about 9 millim. 



nah. Klikitat V., W. T., Thorpe's (10. vii.; S. Henshaw, in Mus. Comp. Zool. Cam- 

 bridge, Mass.). 



Nymph No. III.— PL XXXIX. (whole figure & details). 



Body stouter than in the typical Epliemerella, and with neither tubercles nor spines 

 upon the dorsum ; sternum and venter apparently adapted for adhesion to smooth sur- 

 faces ; antennte remote from the ocelli, and inserted in the angles of right-angled excisions 

 at the sides of the prominent front border of the frons ; first joint of the palpus of 

 maxilla i. about 1^ as long as the second, the terminal joint about \ as long as these 

 combined. — Body broadest at the mesothorax, narrowed in front ; abdomen somewhat 

 oniscoidal, broadest at the third and fourth segments ; the pleurte in segments 2-8 broad 

 and relatively short, concave above, strongly rounded off in front, their outer margins 

 less curved and meeting their oblique posterior margins at an acute angle ; the 

 pleurae of segment 9 naiTower and posteriorly more acute, the segment in dorsal view 

 resembling somewhat a mitre with the cleft choked seen sideways ; dorsum strongly 

 arched, furrowed obliquely at the sides in segments 2-7 by grooves which ascend singly 

 from their front margins at the bases of the pleura?. These grooves are displayed in 

 fig. 2. Venter densely velutinous, and ('exclusive of the pleuree) elongate-ovate, almost 

 plane behind (the pleurae being only very slightly jjrominent), but with a deep arclied 

 depression in front of the third segment, wherein is situated a smooth nude curved 

 transverse furrow immediately adjacent to the anterior velvety boundary of the adhesive 

 surface. This furrow is probably the channel for the readmission of water into the 

 enclosure when the insect desires to be free after adhesion has been established. Beneath 

 the thorax are two large and deep nude concavities, bounded by prominent sharply 

 defined even margins, and divided from one another in front of the mesosternum; the 

 anterior is widened angularly close behind the fore coxae; the posterior resembles the 

 impressure of an axe-head laid flat, edge towards the tail. Pronotum transverse, widest 

 behind ; its posterior lateral angles acute. Head vertical, transverse ; in front view 

 quadrilateral, slightly oblong and flattened ; frons prominent and truncate in front 

 (where it projects in advance of the mouth-parts), angularly excised at its anterior 

 angles, and with nearly parallel sides ; antennae short ; mouth-parts similar in type of 

 construction to those of Epliemerella. Legs moderately long ; femora flattened behind, 

 spinulose or denticulated along their edges ; hind tarsus about f as long as the tibia. 

 Tracheal brancliise arranged as in Ephemerella, but their laminae more obtuse. Length 

 of body, ? , 11, seta3 4 millim. 



Hah. Colorado, in a brook at Idaho, adhering to the underside of a board, 5th July; 

 Roaring Water Fork, Col., 2nd August, Lt. Wheeler (Mus. Comp. Zool. Cambridge, 

 Mass.). 



