326 
Psyche 
[December 
differences are due to different stages of development, but in any case 
the respiratory system of the nymphs was clearly highly adapted for an 
aquatic life. In this connection, reference should be made to the pres- 
ence of lamellae along the sides of the abdominal segments. In Recent 
nymphs the lamellae occur at the junction of the terga and sterna, 
extending outward and forming flat, plate-like ridges along the pleural 
region of the segments. In those protereismatid nymphs which show 
the pleural region of the segments lamellae appear to be present, also. 
They may be homologous with similar structures which have been 
known for many years along the sides of the abdomen of adult Paleo- 
dictyoptera and Megasecoptera and which have often been interpreted 
as persistent, vestigial gills. 
The cerci and the caudal filament of the protereismatid nymphs are 
strikingly like those of some Recent mayflies, even to the arrangement 
of the long hairs. There appear to have been no basic changes in the 
nature of these structures since Permian times, except in a few of 
the most highly specialized Recent genera. 
The mandibles are unfortunately known in only one nymph (Okla- 
homa nymph no. i). In that specimen they are surprisingly large 
and broad, with well-developed teeth. The mandibles of existing may- 
fly nymphs are diversely adapted but none appear to be as large or 
as massive as those of the fossil. In all probability protereismatids were 
predaceous. 
In summary, it can be stated that the Permian protereismatid may- 
fly nymphs (so far as known) were adapted for aquatic life, having 
well-developed gills on the first nine abdominal segments; that they 
had walking instead of swimming legs, with five segmented tarsi, and 
that the nymphal wings developed in a lateral-posterior position, 
being connected to the thorax only along the articular region of the 
wing. 
References 
Brauer, F., J. Redtenbacher and L. Ganglbauer 
1889. Fossile Insekten aus der Juraformation Ost-Sibiriens. Mem. de 
l’Acad. Imp. Sci. St. Petersburg, 7 ser. 36 (15): 1-20. 
Carpenter, F. M. 
1933. The Lower Permian Insects of Kansas. Part 6. Proc. Amer. 
Acad. Arts Sci., 86: 411-503. 
1947. Lower Permian Insects from Oklahoma. Part 1. Proc. Amer. 
Acad. Arts Sci., 76: 25-54. 
1963. Studies on Carboniferous Insects from Commentry, France. Part 
IV. The Genus Triplosoba. Psyche, 70(2): 120-128. 
Clemens, W. A. 
1915. Mayflies of the Siphlonurus Group. Can. Ent., 47: 245-260. 
