122 TERTIARY INSECTS OP NORTH AMERICA. 



3. EPHEMERA MACILENTA. 



PI. 12, Figs. 4, 10. 



Larva The body is stout but not so stout as in the last species, which 

 is only slightly larger than this ; it tapers also in a similar manner but is not 

 so rounded anteriorly. The head and mandibles are of similar form and 

 size, but the head is not so distinctly separated from the thorax as in that 

 species, being continuous with the general outline of the body. The legs 

 are considerably shorter than in the preceding species, but while agreeing 

 with them in general structure the femora are stouter in relation to the 

 tibia;. The abdomen is similarly marked, but the stripes are shorter, reach- 

 ing neither the anterior nor the posterior margins of the segments. The 

 caudal seta? are of equal length, nearly half as long as the body, and fringed 

 on either side with short cilice, scarcely longer than the breadth of the seta. 



Length of body, 1.75 mm ; breadth of thorax, 3.G mm ; of head, 1.85 mm ; 

 length of fore tibia, 1.9 Q1IU ; breadth, 0.35 mra ; length of hind tibia, 2 mm ; 

 breadth, 0.35 mm ; length of caudal seta?, 7.5 mm . 



The brevity of the legs and the uniform brief ciliation of the caudal 

 setae distinguish this species from either of the other larvae here described. 



Florissant. Five specimens, Nos. 232, 1137, 7280, 10423, 1352G. 



4. EPHEMERA PUMICOSA. 



PI. 12, Figs. 7 (pupa), 15, 16 (larvn). 



Larva. This species is both smaller and slenderer than any of the larvae 

 described above. It tapers in the same manner as the others, except in being 

 more rapidly expanded at the thorax and in having the abdomen of more 

 uniform width, a peculiarity seen also in the nymph referred to the same 

 species. As in the other species, the head is of the same width as the ex- 

 tremity of the abdomen. The legs are poorly preserved in all the speci- 

 mens, but seem to agree entirely with their appearance in the nymph. The 

 abdomen is marked as in E. immobilis, but if anything with longer and 

 straighter stripes. All the caudal seta? are of similar length, slender, but 

 rather short, being only about one-third the length of the body ; they are 

 furthermore distinguished from those of the other species by being naked, as 

 far as can be seen, though one specimen seems to show an apical bristle on 

 either side at the end of each joint of the middle seta. 



