48 CONNECTICUT GEOL. AND NAT* HIST. SLAVEY [Bull. 



to the base of the wing, is called the dorsopleural or notopleiiral 

 suture. 



The scutum, according to the dipterists, is the area, so, behind 

 the transverse suture, ^^.s- of Fig. 6, C, but this region is not the entire 

 scutum, since the anterior region of the scutum, asc of Fig. 6, A, com- 

 bines Avith the tnie prescutum, pse of Fig. 6, A. to form the so-called 

 prescutum, j)sc of Fig. 6, C, as was mentioned above. It should there- 

 fore be understood that the region labelled jjos in Fig. 6, A, or that 

 labelled sc in Fig. 6, C and E, is in reality only the posterior portion 

 of the entire scutum, and is referred to as the "scutum" merely for 

 convenience, in order to avoid further increasing an already very 

 extensive terminology for the external morphology of the Diptera. 



The parascutellum, pas of Fig. 6,C, and of Fig. 7,1, is an area of 

 the scutum lying on each side of the scutellum, s7. Its surface is 

 usually somewhat declivitous, and in some Diptera it forms a trough- 

 like area on each side of the scutellum. It comprises a fairly large 

 area in the higher Diptera (Fig. G, C) but is greatly reduced in those 

 insects in which the scutellum is small (Fig. r),D). 



The scutum bears the dorsal wing processes, or dorsal pivotal 

 points involved in the movements of flight. The anterior wing- 

 process is formed by the suralar sclerite, labelled sm. in Fig. 7.1, 

 while the posterior wing process is formed by the so-called adanal 

 pi-ocess, labelled anp in Fig. 7, 1. The axillary sclerites, referred to 

 later, are situated between the bases of the wing-veins and these 

 processes of the scutum. 



The following designations are applied to certain features of 

 the scutum by writers on chaetotaxy. The small ridge on each side 

 of the scutellum, connecting it with the scutum, is called the scutellar 

 bridge. The swollen, antero-lateral area of the scutum, lying just 

 behind the lateral ends of the transverse suture, and antero-mesad of 

 the bases of the wings, is called the prealar callus; while the postalar 

 callus is a tubercle between the scutellum and the wing, which, accord- 

 ing to Imms (1929), "constitutes the prominent posterodorsal an^gle 

 of the scutum." The supraalar groove or cavity is the lateral groove 

 extending along the scutum immediately above the attachment of the 

 wing; while the alar frenum, according to Comstock (1924), is "a 

 little ligament dividing the supraalar cavity into an anterior and 

 posterior part." 



The scutellum, si, is the posteriormost, median sclerite of the 

 wing-bearing plate: and according to some entomologists, the scutel- 

 lum includes not only the median region labelled si in Fig. 6, but also 

 the lateral region, pas, as well. It is preferable, however, to restrict 

 the designation scutellum to the median region, si. alone. There is 

 usually an anterior and a posterior ridge on each side of the scutel- 

 lum, to give it more rigidity; and the parascutellum lies between 

 these two ridges, adjacent to the scutellum. The posterior ridge 

 usually forks a short distance from the edge of the scutellum, and 

 the anterior arm becomes folded over forward, while the posterior 

 arm follows the posterior margin of the w^ing-bearing plate, which is 



