92 EEV. A. E. EATON ON EECENT EPHEMERID.E OR MAYFLIES. 



it were, the chord of this arch ; the subcosta (2), receding iu a bold curve from the radius, 

 approaches the summit of the same arch, and then takes a nearly straight course, sub- 

 parallel with the larger segment of the costal border, to terminate obliquely in the 

 margin rather near the extremity of the radius. Hence the marginal area of that wing 

 is sublinear, dilated in front at the base, and acuminate at the point ; while the sub- 

 marginal area is broadest in its first j, and thonce is gradually narrowed in a slight 

 degree to its oblique, roundly truncate extremity. Cross veinlets abundant, present, 

 but often weak, in the marginal area of the fore wing before the bulla. The longitudinal 

 nervures are furnished with branchlets along the terminal margin, which are partly 

 simple and curved, and partly common to both of the adjacent nervures ; there are no 

 isolated veinlets. In the anal-axillar interspace of the fore wing, the two long intercalar 

 nervures communicate mutually by means of cross veinlets, and exhibit the greatest 

 possible diversity in their ultimate destination inwards. Either of them may be the longer 

 of the two, and may annex itself to either the anal or the first axUIar, while the shorter 

 remains abrupt ; or both of them may annex themselves to the one or the other of these 

 nervures ; or each of them may annex itself to that nervure to which it is nearest ; or 

 both may terminate abruptly, communicating with those nervures by means of cross 

 veinlets only. This last arrangement prevails in our native species ; but the variations 

 from it, noted above, are quite independent of species and sex, and are apt to mar indi- 

 vidual symmetry. Guard at the orifice of the mesothoracic spiracle small and triangular. 

 Forceps-limbs of d essentially 3-jointed (a minute terminal 4th joint is of occasional 

 individual occurrence) ; the proximal joint normally much longer than the remainder, 

 compressed and dilated towai'ds the base ; the dilatation, usually gradual and at the 

 lower edge, is in L. mollis sudden and superior. The species L. i^rcepedlta, provisionally 

 i-eferred to this genus, has 4-jointed forceps-limbs with a short joint at the base, like 

 CJioroterpes. Abdomen proportioned nearly as iu AlalopJdebia ; the deflexible basis of 

 the 6 forceps, and the homologous lobe in the 2 , are deeply and sharply excised or 

 bifid, with acute triangular points. Median caudal seta subequal to the others ; outer 

 setae in d about 1\ as long as the body, in $ nearly of equal length with the body. 

 Tarsal ungues all dissimilar each to the other. Fore tarsus of <s little longer than the 

 tibia, which is nearly of the same length as the femur ; tlie joints in diminishing sequence 

 rank 2, 3, 4, 5, and 1. Fore tarsus of $ about \ as long as the tibia, which is little 

 longer than the femur ; its joints rank 2, 3, 5, 4 ; hind tarsus (exclusive of joint 1) 

 almost \ as long as the tibia and joint 1 combined; its joints rank 5, 2, 3, 4; the first 

 joint is obsolescent in these tarsi. Nymph latent ; abdominal tracheal branchite uniform, 

 bipartite, inserted at the latero-dorsal angles of the segments ; their divisions simple, 

 subulate or linear-acuminate, beset with minute distant hairs ; the hinder pairs in repose 

 widely divergent backwards from the sides of the body. Caudal setae nearly 1^ as long 

 as the body, and, like the setaceous antennae, provided with verticils of minute spreading 

 hairs at the joinings. Fangs of the mandibles strong and acute; appendage (eudopoditej 

 well developed, terminating in a compact oblique brush. Palpus of maxilla i slender; 

 its last 2 joints together constitute about | of the whole, Lacinia of maxilla ii acutely 

 eemi-ovate and narrow, the inner edge rather concave. Tongue broadly obovate, retuse 



