1968] 
Kukalovci — Mayfly Nymphs 
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those on the first probably somewhat smaller than the others but the 
ones on the ninth pair much reduced. Dimensions: length of pre- 
served part of body, 17.2 mm; length of left fore wing, 4.5 mm; 
length of right fore wing ; 5.3 mm; length of right hind wing 5.0 mm. 
Discussion : the foregoing nymphs are sufficiently close structurally 
to indicate their membership in a single family; the nature of their 
wing venation indicates that this was most probably the family 
Protereismatidae. Their assignment to one genus is less certain 
but all have been placed in Protereisma since there are at present no 
Fig. 4. Protereisma sp. (nymph no. 3), Lower Permian of Czechoslovakia. 
Original drawing. [Specimen in Charles University, Prague] 
bases for recognition of genera among these Permian nymphs. From 
a survey of all of these specimens it is now possible to suggest char- 
acteristics possessed by the nymphs of the Protereismatidae. The 
head, preserved in only one nymph, was slightly narrower than the 
prothorax and rather long; the eyes were average size, the mandibles 
large with prominent teeth ; the antennae very slender with numerous 
