BY FREDERICK A. A. SKUSE. 597 



know that when he wrote his paper on the terminology, and hence 

 its insufficiency, which he must have felt after he had written it. 

 But Schiner also did not carry out his theory very thoroughly ; in 

 some points it seems to me that he is in contradiction with himself. 



" In the meantime, for ordinary descriptive purposes, we have 

 a nomenclature which is conventional, but nevertheless useful, 

 because it contains as little innovation as possible. In most wings 

 of the Diptera the small or anterior cross- vein is an easily discern- 

 ible object ; it is always placed between the third and fourth veins. 

 We call discal cell the well-known cell in the middle of the wing, 

 although, as I said before, the discal cell of the Orthorhapha is 

 not homologous with that of the Cyclorhapha, We call tirst pos- 

 terior cell, the cell which has the small cross- vein at its basis. All 

 the rest is, in most cases, easily found. But not always, — the 

 interpretation of some venations is very difficult. 



" I can understand, for instance, that you found some difficulty 

 in translating Winnertz's terms into those of Loew. Loew (I.e.) 

 gives no hint whatever about the Mycetophilidse. But in Schiner 

 (V. z.-b. G. Wien, p. 200, tab. 3, fig. 1) we find a figure of a wing 

 of Mycetopliila, with the nomenclature of the venation. The 

 longitudinal veins are : — Mediastinal-ader (Loew's auxiliary vein) ; 

 subcostal-ader (Loew's first longitudinal vein); cubital-ader (Loew's 

 third longitudinal vein) ; then follow the small cross-vein and the 

 fourth longitudinal vein. The second longitudinal vein is wanting, 

 and this a peculiarity of the Mycetophilidse.* 



" In order to verify whether Loew had adopted for the Myceto- 

 philideo the same interpretation of the venation as Schiner (that 

 is, whether he likewise omitted the second vein) I have examined 

 his descriptions of Mycetophilidse in Century IX. (Berl. Ent. 

 Zeits., 1869), and in the Beschr. Europ. Dipteren. I find that, 

 like Schiner, he always took for the third vein (Schiner's cubital), 



* " This occasional absence of one or the other of the longitudinal veins 

 induced Schiner to give them names (Mediastinal, Cubital, etc.), instead of 

 merely numbering them (first, second, etc.). But the latter method has the 

 advantage of priority, having been adopted by Meigen and developed by 

 Loew." — Osten-Sacken, inlitt., 16th March, 1889. 



