1931 ] 
Structure of Notiothauma reedi 
11 
dously reduced — a feature which serves to set apart the 
Bittacidse from the rest of the Mecoptera very sharply. 
In Notiothauma , the gonocoxites cx of figs. 5 and 7, are 
more like the prototypes of the gonocoxites of the Pan- 
orpidse (figs. 8, 23, etc.) than is the case in Chorista (fig. 
12), although Chorista and Panorpodes are not sharply 
set off from the Panorpidss in this respect. In Notiothauma 
(fig. 5) there is an intercrater cc or intercoxal region which 
is hollowed out and sclerotized in a fashion suggesting the 
prototype of the condition met with in primitive Diptera, 
and all of the features of the genitalia of Notiothauma sug- 
gest that the ancestors of the Diptera resembled Notio- 
thauma in many respects. 
In Boreus (fig. 9) the gonocoxites cx are quite large in 
proportion to the size of the gonostyles st, and there is a 
wide posterior, or ventral, intercoxal area ic of membrane 
between the gonocoxites cx. In Nannochorista (fig. 10) the 
gonocoxites cx are likewise very large in proportion to the 
length of the gonostyli st , but the intercoxal area has be- 
come sclerotized and the gonocoxites appear to be quite 
solidly united. In the Bittacidse (fig. 11) the intercoxal 
area has likewise become sclerotized, but a partial suture 
remains to demark the distal region of the gonocoxites, 
which are hugely developed in proportion to the size of the 
gonostyli st. 
In the Panorpid shown in fig. 8, the posterior intercoxal 
area contains a pair of membranous lobe-like valves, the 
postvalvse labelled p in fig. 8. These are apparently homo- 
logous with the posterior valve-like structures labelled p 
in fig. 12 of Chorista and a similar pair of valves labelled 
p in fig. 15 of Notiothauma. The function and significance 
of these postvalvse is not clear. 
In the Panorpid shown in fig. 8, the intercoxal area con- 
tains a pair of ventral phallic valves labelled v, which are 
received in a flanged groove of the gonocoxite cx, and the 
Panorpid shown in fig. 8 likewise has a pair of dorsal phallic 
valves labelled d, which lie on each side of the meatus or 
gonopore, as the genital opening of the male is called. These 
valves may represent the penis valves of sawflies which 
form the sedeagus or chitinous parts about the penis in 
