286 
of sabulosa (= depressa) still remains to 
be discovered, but when found will possess 
anal abdominal gills. 
Claassenia arctica (Klapalek) 
Adelungia arctica Klapalek (1916, pp. 59, 
78). Original description,?é 2. 
Perla lanqguida Needham & Claassen (1925, 
p. 100). New synonymy. 
Claassenia languida Ricker (1938, p. 140). 
Notes on type and generic transfer. 
Acroneuria depressa (?) Claassen (1931, p. 
86 and pl. 27, fig. 207). Misidentification of 
nymph. 
This large western species of stonefly 
has had an interesting bibliographic his- 
tory, considering the few times it has been 
mentioned in literature. It was originally 
described by Klapalek in his new genus 
A delungia, with caudata from China as its 
genotype. In 1925, Needham & Claassen 
in their Monograph described languida 
from specimens from Wyoming and Mon- 
tana, but strangely made no mention of a 
species arctica from ‘Arctic America.” 
Wu (1934) noted that ddelungia was a 
preoccupied name and proposed Claassenia 
as the name to replace 4delungia, without 
any reference to its occurrence in North 
America. Ricker (1938) noted the close 
relationship between arctica and languida 
and placed both for the first time in the 
genus Claassenia. Ricker’s figures of the 
typic specimens in the British Museum 
and studies of specimens in the Illinois 
Natural History Survey collection con- 
vinced me that /anguida is a synonym of 
arctica. Many species occurring in the 
mountains of northwestern states range 
far into Canada. 
Whether the species now included in 
Claassenia form a sufficiently distinct 
group to warrant generic status may be 
questioned, but at least for the present I 
am so recognizing them. 
In August, 1940, while in Yellowstone 
National Park, Wyo., I had an excellent 
opportunity to rear series of arctica, both 
male and female, from nymphs and ob- 
serve some of the habits of the adults. 
The adults are nocturnal and emerge at 
nightfall from nymphs which crawl out of 
the water on rocks or other objects near 
the shoreline of such turbulent mountain 
streams as the Yellowstone River. During 
the day the adults rest under stones and 
other objects close to the water’s edge and 
Itttnotis NATURAL History SURVEY BULLETIN 
Vol. 22, Art. 2 
when active at dusk or night have the 
ability to advance rapidly over the surface 
of the water somewhat like water-striders. 
Mating often takes place as soon as the 
females emerge from nymphal skins, and 
the males are able to recognize nymphs 
destined to be females as proved by at- 
tempts at mating and by waiting for a 
particular female to emerge. 
Claassen (1931) described and figured 
the nymph of arctica under the name of 
“Acroneuria depressa (?).” Certain char- 
acters of this nymph, particularly size, 
occipital ridge and anal gills, in addition 
to locality records, caused me to suspect 
its true identity before actually rearing it 
in 1940. 
Since records of the occurrence of this spe- 
cies are few, and confined to the references 
me 
Fig. 53.—Nymph of Claassenia arctica. 
