Sept., I9I3-] MeLANDER: SYNOPSIS OF DiPTERA. 221 



acters as the convergence or divergence of the minute postvertical 

 bristles, the manner of fracture of the basal portion of the costa, and 

 the intimate structure of the interfrontalia of the head. The form of 

 the proboscis, the structure of the legs, the venation, particularly of 

 the outer part of the wings, and the style of vestiture have been too 

 recently modified, as measured in biologic time, to be of much service 

 in indicating the interrelationships of subfamilies. 



As will be noted the following analytical table makes use of char- 

 acters that are not customarily employed and which require consid- 

 erable magnification for their discernment. A few words will be 

 needed to explain the terminology adopted. The structure of the 

 cheeks, face and front has proved of great assistance in determining 

 subfamilies: not the general shape, but the vanishing details of the 

 proportions of the sclerites making up the head. The cheeks, that 

 lateral portion between the eyes and the mouth, are a complex of 

 several sclerites. Nearest the eye, the facial orbits, what the Germans 

 designate as Wangen, descend from in front, their delimiting suture 

 continuing straight downward or obliquely backward or even parallel 

 with the eye-margin before it vanishes. This part of the cheek, 

 nearest the eye, I have designated the gena, following Dr. Hough's 

 selection of this term in his Muscidae of Somaliland, 1898.1 Next to 

 the gena lies a varying-shaped piece, called by the Germans the Backe, 

 and by Dr. Hough the bucca. The oral vibrissa is always located near 

 the lower front angle of this piece, but the shape of the sclerite varies 

 greatly. In the Opomyzinse it is linear and parallels the narrow 

 gena; in the Milichiinse it is triangular, owing to an oblique extension 

 forward of the lower occiput, in which case the cheek consists largely 

 of this part of the occiput. Where the relative breadth of the bucca 

 and the gena is called for the measurement should be made near the 

 vibrissal angle, but, since the suture between these sclerites vanishes, 

 its course may need to be projected as a continuation of that part 

 present. In many of the Geomyzinae the lateral prolongations of the 

 center of the face are visible beneath the buccse, thus forming the real 

 margin of the mouth. These four sclerites which enter into the com- 

 position of the cheeks, probably originally sharply differentiated, are 



1 The term gena is in Greek geneion, in Italian guancia, in Spanish 

 niejUla, in French joue, and in English joivl. but these cognates indicate 

 merely the cheek in a generic sense. 



