1901.] 245 



above, with .small antcniue, separated eyes but narrow fronts, aucl 

 thorax entirely clothed with silvery pile, are undoubtedly males. Un- 

 fortunately no external genitalia are to be seen. 'J'hat my three males 

 belong to the same species as the live females there can of course be 

 no question. As to the differences, suffice it to say that in both P. 

 atra, Pz., and P. Leackii, Curt., the third joint of the antennae is 

 much smaller in the male than in the female, while a difference between 

 the sexes in the coloration of the hair clothing the thorax is no 

 novelty in the StratiomyiclcB* Another very significant point is the 

 fact that, as has already been shown, the three specimens regarded by 

 me as males emerged from the pupa from six days to a week before 

 the first of the females. f 



The type of the genus Pachygaster, Meigen (llliger's " Magazin 

 fiir Insekteukunde," II [lb03], p. 26G) \^ Nemotelm ater, Fz. In this 

 species the eyes are small, and in the male meet together on the front 

 anteriorly. The head of the female, viewed from the side, has a 

 peculiar flattened and also an elongated appearance, owing to the fact 

 that the posterior orbits are produced on each side into a prominent 

 tumid ridge. In the male this ridge is much more pronounced below 

 than above, and the head is less flattened from above downwards. In 

 Pachygaster Leachii, Curt., the eyes are larger and more prominent 

 in both sexes, while the posterior orbits are not developed at all in 

 the male, and only very slightly in the female below ; consequently 

 the head of P. Lcachii is very different in shape from that of P. atra. 

 Whether, owing to the undeveloped condition of the posterior orbits, 

 and the differences in the size and shape of the eyes and head generally, 

 P. Leachii should be allowed to remain any longer in the same genus 

 as P. atra (although the males of both species are holoptic), is a 

 question beyond the scope of the present paper, and one that may 

 be safely be left to be decided by Mr. "Verrall in the next volume of 

 bis " British Flies." As regards Pachygaster meromelceiin, however, 

 there can be no doubt at all that, since the eyes in the male are sepa- 

 rate, the species cannot possibly be congeneric with Pachygaster ater, 

 but must be referred to a new genus. I therefore propose for it the 

 name Neopachyg aster, and the new genus may be briefly characterized 

 as follows : — 



Neopachygasxkb, gen. nov. 



Agreeing generally (venation, shape of tiody and antennce) with Pachy- 



* The common Odontomyia viridula, Fabr., may serve a.s a case in point. 



t Whether it is the rule among Diptera for the males to appear before the females I am un- 

 fortunately unable to say, but in some cases they certainly do so. Thus in a recent communication 

 Dr. T. L. Bancroft, of ISurpcngary, Queensland, who for some years past has made a special study 

 of Cidicido-, writes as follows : — " in bleeding out mosquitoes I have observed that the first 

 imagines to appear are males ; they emerge several days before the remainder, which are females." 



