[N^O. 64] DIPTERA OF COXXECTICUT : MORPHOLOGY 47 



Transverse, internal, shelf-like projections, called phragnias, 

 furnish points of attachment for the lonoitndinal dorsal muscles 

 which arch the notum in the movements of flight, and their ventral 

 ridges mark the anterior and posterior limits of the segments, in the 

 dorsal region of the segments of insects in general. The postscutel- 

 lum of the mesothoi'ax bears a large, well-developed phragma (called 

 the postphragma ) . to which are attached certain of the longitudinal 

 muscles extending to the prescutal region of the notum. The phragma 

 borne on the anterior region of the prescutum (called the prephrag- 

 ma) is greatly reduced in the Diptera. Other names are sometimes 

 applied to these phragmas, but since they are internal structures, they 

 are of little interest to taxonomists, and are but seldom referred to by 

 dipterists in general. 



The sclerite called the prescutum in the Diptera (i. e., psc of 

 Fig. 0, C) is not exactly homologous with the sclerite designated as 

 the prescutum in the Hymenoptera, etc., since the true prescutum is 

 the region labelled 2^sc in Fig. G, A, to which are attached the dorsal 

 longitudinal muscles extending to the postscutellum; and the prescu- 



1 tal suture (notaulices of Hymenoptera), demarking the true prescu- 

 tum, is either reduced to the small remnant labelled />.s.s in Fig. 6, B, 

 or is completely obliterated in most Diptera. This vestige of the 

 prescutal suture is sometimes called the '"pseudosuture" ; and the 

 prescutal pits, psp of Fig. 6, A. whicli are called the pseudosutural 

 foveae or humeral pits, indicate the true position of the prescutal 

 suture formerly occurring in this region (but later lost in typical 

 Diptera). These pseudosutural foveae, and the paired dots (one on 

 each side of the mid-dorsal line) occurring in the anterior region of 

 the prescutum, and called the tuberculate pits, are features of some 

 importance in the classification of the Tipulidae. The character of 

 tlie narrow, marginal sclerite, pat of Fig. G, A, called the paratergite, 

 is also a feature of some value in the classification of the Tipulidae. 

 In the Hymenoptera the so-called transscutal suture, or cleft, 

 divides the scutum into an anterior and posterior region; and in the 

 Diptera the corresponding suture, ts of Fig. 6, A, C and E, is called 

 the transverse suture. The transverse suture may be incomplete in 

 some Diptera, wdiile in the Tipulidae it forms the so-called V-shaped 



f suture, ts of Fig. 6, A. The anterior region of the scutum, asc of 

 Fig. 6, A, lying in front of the transverse suture, ts^ merges with the 



I true prescutal region, psc of Fig. 6, A, to form a composite area which 

 is usually called the "prescutum"' in the Diptera (i.e., psc of Fig. 6, 

 C and E), and although this region is a pseudoprescutum not strictly 

 homologous with the true prescutum of other insects, there is no 

 serious objection to applying this designation, to it in the Diptera, 

 for the sake of convenience. 



The notopleural region, labelled npl in Fig. 6. C, forms a sunken 

 area sometimes called the presutural or sutural depression in the 

 muscoid Diptera. in which the area in question may bear the so-called 

 notopleural bristles. The cleft, or suture, just below the label, npl 

 in Fig. G,C, extending from the humeral callus or postpronotum. ppn. 



