Introduction. 11 



ils formation must be bom in mind. In such cases tiie posterior cells 

 are also more or less confluent, as the branches which should separate 

 them are absent; generally the first, as usiial, lies above the discai 

 vein, the space outwards to the discai cell is answering to the second 

 and third, the fourtli is coalesced with the discai cell, the fifth on 

 the contrary is always found in the convex postical fork, and oughl 

 aiways to be termed the fiflh, notwithstanding the number of actually 

 present posterior cells. 



With regard to the squamulæ I quite follow the terms used by 

 Girschner (Ueber die Postalar-Membran der Dipt., Illustr. Zeitschr. fiir 

 Entom., 1897, 534); the squamula sitting on the base of the wing, and 

 which in rest lies above the other, is the alar squamula, that sitting 

 on thorax and in rest lying below the alar squamula, is the thoracic 

 squanmla ; the angle formed between the two squamulæ when the wing 

 is stretched horizontally out is the squanuilarangulusorshort, theangulus. 



Finally I shall remark here that the terms used in describing the 

 mouth parts in the larvæ must not be taken as indicating sure homo- 

 logies with the similarly termed parts in the imagines. 



Concerning the system I intend to follow. chiefly at all events, 

 that of Brauer sucli as it is given in the „Katalog der palaarktischen 

 Dipteren von Becker, Bezzi, Kertész und Stein." — When I make the 

 beginning with the Orthorrhapha brachycera, this is of a purely practical 

 reason because our fauna of Nemalocera requires renewed material 

 before it can be worked out. 



As mentioned above I have had material from all the imporlant 

 parts of Denmark: yet the material, as naturally must be expected, 

 is for far the greatest part collected in the environs, nearer or more 

 remote, of Copenhagen, or in the whole in North-Sealand. In order 

 to avoid repeated explanations about the localities I shall here give 

 a list of most of those in North-Sealand with some short explanations 

 of the nature of the locality: 



Frederiksberg Have. — A public garden with canals in the out- 

 skirts of Copenhagen. 



Ladegaardsaaen. — A small stream at Copenhagen. 



Leersø. — A former lake at Copenhagen now dried up and grown 

 with Salix. 



Damhusmosen. — A fen near Copenhagen, chiefly grown with Salix. 



Utterslev Mose. — A fen near Copenhagen, 



Amagerfælled. — A connnoii near Copenhagen. 



Vesterfælled. — A common at the seashore near Copenhagen. 



