160 MR. J. O. WESTWOOD ON THE LEPIDOPTEROUS 



work, will show the complete irregularity in the position of this discoidal vein and its 

 divisions. 



The large moths of the genus Gastropacha are excellent instances in which the 

 arraDgement which I have endeavoured to establish is shown. In G. repanda (H.-Schaffer, 

 Syst. Bearb. Schui. Eur. pi. xviii. fig. 3), the median vein is seen to have four branches, 

 the upper one of which (c 3*) arises from the third branch (c 3), at the lower extremity 

 of the discoidal cell, whilst the other, upper, accessory branch, my b 5*, arises from the 

 preceding, b 5, far beyond the discoidal cell, forming as clearly a portion of the post- 

 costal system as c 3* does of the median, there being no trace of a discoidal vein within 

 the discoidal cell. 



Aglaope infausta (H.-Schaffer, Syst. Bearb. Schrn. Eur. pi. xiii. fig. 32) presents us with 

 an interesting example, in which the arrangement of Mr. E. Doubleday is excellently 

 shown. Here the last branch of the postcostal vein (b 5) extends to the tip of the fore 

 wings, and the discoidal cell is divided into two nearly equal parts by the discoidal vein, 

 which, extending nearly from the base of the wing, branches into two equal branches 

 (my b 5* and c 3*), leaving the three branches of the median vein at equal distances 

 apart. 



In Leucophasia sinapis (see H.-Sch. op. cit. pi. v. fig. 11) the arrangement of the 

 branches is very instructive. Here, in consequence of the very small size of the discoidal 

 cell, all the branches of the postcostal vein arise quite regularly on the anterior side of the 

 vein beyond the cell, the fifth (b 5) extending to the tip of the wing ; but the two accessory 

 and the three branches of the median vein are all equally independent at their origin at 

 the end of the short oval discoidal cell, and appear to be parts of one system of veins 

 distinct from the postcostal. 



In many of the Geometridse, as may be seen especially in the 9th plate of Herrich- 

 Schaffer's work on European Lepidoptera, vol. vi., not only is the small postdiscoidal 

 cell, as I have called it (cellula accessoria of H.-Sch.), found in the Castnice present, 

 but it is even divided into two cellulets by a more or less oblique cross vein. 



In the Hesperiidse, on the other hand, the discoidal cell of the fore wing is elongate- 

 ovate, and all the branches of the postcostal and median veins, as well as the two 

 accessory branches (b 5* and c 3*), arise from the extremity of the discoidal cell at 

 nearly equal distances apart, without any trace of the discoidal vein within the cell ; so 

 that it is impossible, except from analogy, to determine whither each of the several 

 systems of veins extends. 



The same arrangement is also seen amongst the Heterocerous Lepidoptera, as ia the 

 fore wing of Scardia mediella (H.-Sch. op. cit. vi. pi. Microl. iii. fig. 1), and in Nemotois 

 scabriosella (ib. pi. iv. f. 32). 



In some species of Hesperiidse, however, as in Eudamus (Megathymus) yuccce, the 

 postcostal and median systems are easily distinguished, although their two outer 

 branches, b 5* and c 3*, are united by an extremely slender and angulated veinlet 

 imperfectly closing the discoidal cell. 



Erom the numerous figures given in Pis. XXVIII. and XXIX., it will be seen that 

 the branches both of the postcostal and median veins exhibit much irregularity in their 



