TAXONOMY OF MUSCOIDEAN FLIES — TOWNSEND 21 



When the posterior cephalocele is closed by plates of chitin, these 

 are the triangular median epifrOntal, and the two frontals (frontalia 

 or frontal vitta). 



The frontal sac or ptilinum consists of a great part of the pos- 

 terior cephalocele withdrawn into the interior of the head between 

 the frontals and the antennal ridge. 



The lunula is thus an anterior chitinized portion of this sac or 

 ptilinum. 



The anterior cephalocele is the vesicle of the olfactory lobes. 



The posterior cephalocele is the vesicle of the cerebral hemispheres 

 and their median ventricle. 



In the nymph the median parts of the head capsule lie in a deep 

 cleft between the two lateral lobes or paracephala, and in close prox- 

 imity to the ganglia with which they correspond, so that the head 

 appears to be open on the median line. Sections show this to be a 

 deep infolding of the inner edges of the paracephala ( Lowne). 



The two paracephala (two lateral procephalic lobes), having 

 united on the median line, become the paracephalon of the imago. 



The paracephalon is opened transversely by a horseshoe-shaped 

 suture running up from the cheek border on each side and passing 

 between the antennal ridge and the frontals, bridged by a widely 

 distensible membranous tissue (the ptilinum), on the forward me- 

 dian portion of which is the lunula somite. This suture ends on 

 each side at the cheek groove, which is formed in the integument by 

 the mechanical strain on it when the suture is opened to thrust forth 

 the ptilinum. The suture may be properly called the paracephalic 

 suture, but the writer prefers to employ the term ptilinal suture. 



The following is a detailed statement of the external anatomical 

 parts to be studied in the superfamily Muscoidea, arranged primarily 

 in the order of their importance, and severally in the order of their 

 relative position. The characters of the superfamily are to be found 

 in the various features exhibited by these anatomical parts, and are 

 pointed out so far as possible under each head. The parts preceded 

 by i) afford characters of family, subfamily, tribal, and partly gen- 

 eric value, and those preceded by 2) characters of mainly generic 

 value. The terminology is made to conform so far as possible to 

 that already in use. New terms are introduced only in such cases 

 as demand their use for reasons of clearness, conciseness, and per- 

 manence, and for such few parts as had no name and afford charac- 

 ters of taxonomic value. 



The figure here introduced is diagrammatic and intended to show 

 the main sclerites of the front aspect of the head, the characters 

 afforded by which take rank over all others for taxonomic use within 

 this superfamily. 



