426 NEW YORK STATE MUSEUM 



Nymph. Length 8 mm; setae 4 mm additional; abdomen 4.5 mm ; 

 antennae 1.5 mm. 



Head twice as wide as long; thorax convex; legs short; tibia about 

 equal in length to the tarsus without its claw; abdomen depressed, 

 widened on the fourth to ninth segments, with thin lateral margins, pro- 

 duced at the hind angles into thin, flat teeth, which appear in outline 

 like the teeth of a circular saw ; third segment with a minute tooth, first 

 and second segments with none at all, loth segment with a low, longi- 

 tudinal, lateral carina; setae fringed in the middle, nearly naked at both 

 ends. 



Color dirty yellowish, darker above, paler beneath. 



Gills double, well developed on the fourth to the sixth segments, rudi- 

 mentary on the first and seventh, and absent from the second and third ; 

 the opercular anterior leaf on the fourth segment covers all the gills pos- 

 terior to it; on the fifth and sixth segments the anterior leaf is similar in 

 form but smaller and much thinner ; the delicate posterior leaf on the 

 fourth, fifth and sixth segments is two parted ; on the first segment is a 

 simple cylindric rudiment, jointed on a low pedicel ; on the seventh 

 segment the rudimentary gill is leaflike, single, six lobed. 



July 19 quite a number of nymphs were obtained, both from Little 

 Clear creek beside the hatchery and from the hatchery troughs. 



Caenis diminuta Walker 



1853 Caenis diminuta Walker, List neur. ins. Brit. mus. 3 : 584 



1861 Caenis diminuta Hagen, Synopsis Xeur. N. Am. p. 55 



1861 Caenis arnica Hagen, Synopsis Neur. N. Am. p. 55 



1871 Caenis diminuta Eaton, Ent. soc. Lond. Trans, p. 95 (description 



in Latin) 



1885 Caenis diminuta Eaton, Linn. soc. Lond. Trans. (2) 3 : 147 (a full 



description) 



1892 Caenis diminuta Banks, Am. ent. soc. Trans. 19 : 348 (listed) 



This dumpy, little, nocturnal species was taken abundantly in a trap 

 lantern hung on the side of the boathouse at the outlet of Little Clear 

 pond. 15 to 50 specimens were taken at a single lantern each evening 

 from the 14th to the i8th of July. This appeared to be the season 

 of greatest abundance for the species. It is quite variable in size 

 and in coloration : the best colored of my specimens agree well with 

 Eaton's detailed description ; but the size is often much larger, reaching 

 5-6 mm in length. This may be due to the taking of published measure- 

 ments from dried specimens, which are always shriveled considerably. 

 The species is generally distributed over the eastern United States. 



The nymphs are common among the trash on the bottom in all quiet 

 waters. Their inconspicuous coloration and trashy covering protect 



