52 Annals Entomological Society of America [Vol. IX, 



for a part of the pleuron (Figs. 2 and 11, psl, prsc). These 

 prolongations of the tergum are usually lacking in the lower 

 forms. In other insects they may be much reduced in size 

 or split up into smaller pieces. 



The episternum and epimeron are separated externally by a 

 suture, termed the pleural suture, which extends from the 

 pleural wing process or fulcrum to the pleural coxal process 

 (Fig. 1, plss). Internally these two sclerites may be readily 

 distinguished from each other by a strongly chitinized ridge 

 variously termed the pleural ridge, entopleuron or apodeme, 

 which likewise extends from the pleural wing process to the 

 pleural coxal process. 



The pleuron bears three processes which usually have an 

 inward projection for the attachment of muscles. Above is the 

 pleural wing process which serves for the articulation of the 

 wing (Fig. 2, plwp). It consists of a dorsal prolongation of the 

 pleuron, of variable length, through which runs the pleural 

 suture externally and the entopleuron internally. On the lower 

 margin of the pleuron is the pleural coxal process, with which 

 the coxa articulates (Fig. 4, cxp). It is similar to the pleural 

 wing process and has the pleural suture and pleural ridge 

 extending through it. The pleural process or pleural arm 

 (Snodgrass, '10) is situated a short distance above the coxal 

 process. It projects inward and downward from the ento- 

 pleuron. Usually it rests against the furca (an inward pro- 

 jecting process of the sternum, termed the apophysis) and 

 frequently fuses with it (Fig. 12, f). 



Along the dorsal edge of the pleuron are generally found 

 three or four small sclerites. Two of these, the basalar plates 

 (Crampton, '14) are generally found in front of the pleural 

 wing process, and are termed by Crampton, '14, the anterior 

 and posterior basalar sclerites, terms which will be used in this 

 paper (Fig. 2, pba, aba). Behind the wing fulcrum there is 

 usually one, sometimes two of these sclerites, which are termed 

 subalar plates (Crampton, '14, Fig. 2, sa). Lowne, '90, in his 

 book on the Blow-Fly, terms the subalar plate, the "costa. " 

 Snodgrass, '08, terms it the " postepimeron " and Crampton, '09, 

 the posterior "costal sclerite. " Verhoeff termed the anterior 

 basalar plate, the " alarpleura. " Snodgrass, '10, termed all 

 these plates the "paraptera. " Those situated in front of the 

 wing process, he called the preparaterum or episternal paraptera 



