554 MAJOR E. E. AUSTEN ON THE 



it is perhaps worth while to recall that the preliminary stages of 

 Xylophagidte and Coenomyiidse are also associated with trees, 

 albeit in a dead or mouldering condition, the larvfB, which in 

 the case of the two latter families are carnivorous and predaceous, 

 living in decaying wood and under bark. 



(e) Bodily Dimensions in Pantophthalmidie compared with those 

 of Exceptionally Lccrge Diptera belonging to other Families. — 

 Giantism. 



Although, as will be seen directly, in wing-expanse, and of 

 couise in length of leg, Pantophthalmidte are surpassed by 

 certain Tipulidse of abnormal size, while length and wing-expanse 

 in the largest species are about the same as or somewhat below 

 the corresponding dimensions of the largest representatives of the 

 Mydaidte, the members of the present family as a whole are 

 undoubtedly by far the bulkiest, and therefore the largest of all 

 Diptera. 



Among slenderly built Diptera, the largest forms are to be 

 found in the Tipulidae, wherein, as regards actual size, certain 

 species of the genus Gtenacroscelis Enderlein are probably Avith- 

 out existing rivals. Thus, a male belonging to a variety of 

 Ctenacroscelis brobdignagius Westw., from China (N.-W. Sze 

 Ohuen), just over 39 mm. (1| inch) in length, has a wing-expanse 

 of 104 mm. (rather more than 4 inches), while the outstretched 

 legs cover an area at least 6| inches in length by 5 inches in 

 breadth. 



Although the family Mydaidse includes a number of species, 

 the representatives of which are of moderate dimensions, certain 

 members of the genus Mydas, which are among the largest 

 of Diptera, are relatively gigantic. By way of illustration, 

 mention may be made of Mydas prwgrandis Austen, a male of 

 which from Brazil has a wing-expanse of 85 mm. (between 3;| and 

 3^ inches), while the length of this insect, exclusive of the long 

 and prominent antenna), is 48 mm. (between 1| and 2 inches) "-\ 

 The dimensions of this species, in fact, as represented at any rate 

 by the type and paratype (both males) in the National Collection, 

 are but slightly larger than those of the somewhat aberrant re- 

 presentative of the Pantophthalmidae originally described by the 



* Writing with reference to what is almost certainly the female of this species, 

 of which ho gives a life-size illustration derived from a photograph, Williston 

 (N. American Diptera, pp. 16, 17, fig. 1, 1908) furnishes considerahly higher measure- 

 ments, remarking : — " The largest specimen of a iiy of which I have knowledge is 

 that figured herewith natural size, pertaining to an indeterniinahle species oi Mydas 

 from South America. The length of this specimen from the tip of the antennee to 

 the extremity of the abdomen, is sixty-seven millimeters, or, omitting the antennie, 

 iifty-two millimeters ; the expanse of wings one hundred and seventeen millimeters, 

 or a little more than four and one-half inches. The smallest dipteron that I have ever 

 observed in the examination of many thousand specimens and five or six thousand 

 species, is a cecidomyid measuring a trifle less than one-half millimeter, also omitting 

 the antennse. In other words, the Mydas is more than one million times the size 

 of the cecidomyid. Possibly there are still greater discrepancies between the largest 

 and smallest specimens of the order, but in all probability not much." 



