No. 64] DIPTERA OF CONNECTICUT : MORPIIOLOOY 55 



his tf-rms siicli as "mesopleura'' and "metapleiira" cannot be restricted 

 to the parts so desicrnated by him, and the area which he designates 

 as the "hypopleiira-' is an unnatural conglomeration of parts of the 

 ? mesothorax and metathorax, combined. An examination of the figure 

 on page 503 of the paper by Osten-Sacken (1884) — whidi was taken 

 from a figure by Mik (1882) — will show that what Osten-Sacken here 

 calls the "hypopleura"' is, in reality, the mesothoraeic meropleurite, 

 mpl., together with the metathoracic episternum, <?.s, and epimeron, 

 em, of Fig. 6, C (of the present paper); and this application of the 

 term hypopleuron is adopted in the textbooks of Imms (1929, Fig. 

 565), Tillyard (1926, Fig. W 12), and others, although Aldrich and 

 Darlington (1908) apply the term "hyposternum" to this area. Willis- 

 ton (1908, Fi,g. 8) and'Verrall (190*1, Fig. 122), on the other hand, 

 restrict the term ''hypopleura'' to the metaplcuron alone, while Corn- 

 stock (1924) in his Fig. 1001 (taken from Kiley and Johannsen) ap- 

 pears to use the designation "hypopleura"' for the meropleurite of 

 the mesothorax, although the metapleuron may possibly be included in 

 ' Comstock's "hypopleura-', since the limits of the area in question are 

 ![ not clearly defined. Back (1909) applies the designation "hypo- 

 pleura" to the pleurotergite (i. e., the areas labelled spt and ipt in 

 Fig. 6, C) in his Fig. 2 (Plate 2) of the thoracic sclerites of an asilid, 

 and other taxonomists employ the term "hypopleiira" in so many dif- 

 ferent ways that there is no uniformity of usage even when a purely 

 conventional terminology of this kind is employed, and a more exact 

 terminology based upon comparative morphology is much preferable 

 to that suggested by Osten-Sacken, which has no significance from 

 the latter standpoint. 



The Mesosternum. The mesosternum is relatively small and un- 

 important in most Diptera. In the tipulid Gnopliomym tristissima 

 (Crampton, 1925b, Plate 3, Fig. 8) the mesosternal region contains a 

 ; presternum, basisternum, and furcasternum, with the latter divided 

 i into an anterior and posterior division by a transverse suture. The 

 basisternal region, hs of Fig. 6, A and B, may be external, or it may 

 l>ecome inrolled along the median ventral line to form an internal 

 median partition in front of the furca, or paired apophysis of the 

 sternal region. In such cases, the lower portion of the episternum, 

 kes of Fig. 6, C, extends downward toward the mid-ventral region of 

 the mesothorax. 



The furcasternum (or sclerite bearing the furca) does not, as 

 a rule, participate in the inrolling process, but frequently becomes 

 folded between the coxae as these approach each other in the mid- 

 ventral region. A wing-like lateral extension (one on each side) is 

 frequently given off by the furcasternal region, and extends along 

 the mesal surface of the middle coxae to furnish a ventral pivotal 

 point for the coxae when the latter are mobile, 



5. The metathorax 



The metathorax of the Diptera was regarded as the representa- 

 tive of the median segment, or first abdominal segment of the Hymen- 



