262 
Psyche 
[September 
what larger mandibles is located anteriorly from the maxillae and 
there is the fifth stylet, probably derived from the hypopharynx, be- 
tween the maxillae and slightly more posterior. 
The arrangement of the stylets in Monster opt erum moravicum 
fully confirms the conclusion of Carpenter and Richardson. The pair 
of mandibles is superimposed, and slightly longer than the pair of 
maxillae. The mandibular stylets in all probability partly overlap 
each other along the inner margin, because the undisturbed width of 
the left mandibular stylet (fig. 7-Md) extends much beyond the ideal 
median line. The same madibular stylet probably exposes in this part 
(fig. 7-Md) its natural inner surface where it contacts the maxillary 
stylets. It is provided by alternating ridges and grooves (fig. 8-R, G) 
probably enabling firmer connection in between stylets and strengthen- 
ing the long stylets. 
The rest of the beak (more proximal and right part in fig. 7) 
shows the inside surface of the cavity in the mandibular stylets. It 
seems certain that the mandibles were hollow, as in Recent dragon- 
flies (P. S. Corbet, in litt.). The mandibles of other extant insects 
are mostly solid except for occasional cavities and canals containing 
nerves for sensillae and haemolymph. The hollow nature of the 
elongated mandibles of the Palaeodictyoptera may be explained as a 
means of reducing the mass of the head. This assumption seems an 
acceptable solution for the mechanical problems of flight engendered 
by the considerable weight of the head when compared to the rest of 
the body. 
In the cavity inside the mandibular stylets, there are 5 rows of 
deep crescent-shaped pits (fig. 7-P; 8-P) and oval elevations (fig. 7-E; 
8-E). They form continuous rows and seem to belong to a single 
structural unit, which is a series of short, peg-shaped, perpendicu- 
larly oriented pillars, supporting the long hollow mandibular stylets 
from inside. This assumption is based mainly on the fact that the 
second row of crescent-shaped pits (fig. 7-P) passes distinctly under 
the layer Md (fig. 7), which is the natural surface of the mandible 
in contact with the maxillary stylet. On the Md layer the pit row 
continues in the form of oval elevations (fig. 7-E). 
The left maxillary stylet is completely missing; the right is pre- 
served only by the fragment of distal end (fig. 7-Ma). However, 
it provides information on the morphology of the mouthparts in 
Palaeodictyoptera: the maxillary stylets were located under the man- 
dibular stylets (in fig. 7 reversed because of the ventral view of the 
beak) ; they were distinctly shorter than the mandibles; they were 
