LUCY WRIGHT SMITH 
465 
Ny7nphs 
It is not possible at the present time to more than mention the 
nymphs of this tribe. Since I have no life history material I have 
been able to recognize only those nymphs which belong with the 
gill-bearing species. Of course the form and location of the gills 
is characteristic. The shape of the head is distinctive also, being 
curiousy broadened laterallj^ bj' very large maxillae. In the 
following specific descriptions two nymphs are described in detail. 
• MorpJwlogical Notes 
This group, like P ter onar cello , is so little known as yet that it 
has not been studied from biological or morphological view- 
points. At the end of Hagen’s description of Megarcys (Dictyo- 
genus) signata he commented upon the fact that the species was 
of special interest, as an exception to the genus, since it was 
gill-bearing in the adult, that the hitherto-known species (all 
exotics) were without them. Among the following descriptions 
of additional North American species a number of other gill- 
bearing images will be found. 
Judging alone from the appearance of the external genitalia of 
the males of this tribe one would not imagine that a close rela- 
tionship existed between them. But dissections of the supra-anal 
plates show not only that the fundamental plan of all of them is 
identical, but also that it is similar to that of Pteronarcella and 
the proteus group of Pteronarcys. This tribe appears to have 
reached a higher degree of specialization in at least one respect, 
that is in the more complicated form of the outer portion of the 
free end of the supra-anal plate. In all of these (figs. 40, 45, 50) 
it is made up of three parts, which I am calling the median and 
lateral stylets. The paired ones are joined to the median one at 
the bases only, but they appear to have a secondary connection 
with the para-genital plates, being bound to them by bands of 
membranous tissue, so that all movements of the plates involve 
the stylets in a similar movement. 
The variety of form in all the stylets is considerable and of 
such a character in some instances as to prevent certain con- 
jectures of function. One can doubtless say with a good deal of 
surety, that whatever their use may be it is as some accessory 
copulatory organ. It does not seem improbable that the median 
TRANS. AM. ENT. SOC., XLIII. 
