170 PROCEEDINGS: BOSTON SOCIETY NATURAL HISTORY. 
sides, and transverse line below, lies a funnel-shaped cavity lead¬ 
ing to the pharynx. Into this space the tips of the flabellal setae 
dip when those organs are depressed. It may be called the buccal 
cavity, and within the transverse line four structures are successively 
differentiated from its floor: a delicate, hair-fringed crest, a black, 
triangular mental sclerite (tr), a complicated saddle-shaped sclerite 
with a median crest and lateral toothed spurs (li), and confluent 
with this last, an arch of heavy chitin which is pierced by the 
orifice of the salivary duct (hyp). The mental sclerite is braced to 
the divergent lines at its lower angles. The arch sclerite, and 
indirectly through it the saddle shaped sclerite, are strengthened by 
a narrow-linear “line” of heavy chitin (pi. 15, fig. 31, htr) which 
crosses the thin chitin of the buccal cavity from the black-spot area 
of either side. These hypopharyngeal traverses give support also to 
the walls of the pharynx by short apodemes. 
The mental sclerite was called “under lip ” by Meinert (’86) and 
corresponds to the structures figured by Miall and Hammond for 
larvae of Chironomus, (’92, : 00) , Miall (’93) for Dicranota, and 
Miall and Walker (’95) for Pericoma as “submenfcum.” Raschke 
identified the fold that I have termed the transverse line with 
the mention, “kinn.” For Miall, the sclerites which correspond 
to the saddle-shaped sclerite of Culex are “mentum.” With Culex, 
however, this sclerite sheathes the bud which forms the labium of 
the adult and is to be regarded as the larval labium. The mental 
sclerite would seem to be either a men turn or a submentum, as ifs 
hypodermis during the metamorphosis passes into the floor of the 
head (pi. 15, figs. 34, 36 ,fold). 
The mandibles have a powerful musculature. Each receives a 
converger muscle on the lower internal angle and a divaricator on 
the lower external angle. These muscles arise by triple heads on 
the walls of the epicranium. Each maxilla has two muscles. One 
consists of two parallel bands and arises near the origins of the 
mandibular muscles (clep max), the other is single and arises from 
the divergent line (retr max). Both insert at the middle of the 
base of the maxilla. The action of these muscles was determined 
with difficulty, but by watching slow contractions in a dying larva 
it was found that the double band pulled the maxilla caudad and a 
little outward (ventrad) while the single muscle pulled the maxilla 
caudad and inward (dorso-mesad). Hence the double muscle may 
