394 R. OSTEN SACKEN 



A work like the present must, of necessity, be considered as 

 only preliminary , preparing materials for monographic work. 

 For this reason, I did not deem it my duty to describe as new, 

 every specimen that I could not determine. The effect of this 

 kind of pseudo-conscientiousness merely is, to add to the mass 

 of scientific rubbish of species duhiae with which dipterology is 

 more afflicted than any other branch of entomology Q). It is not 

 urgent at all, to describe every single species of exotic Sciara, 

 Culex, Anthomyia etc., the more so as the european species of 

 these genera are as yet insufficiently known. Even the detailed 

 working out of such genera as (in the present instance) Ta- 

 banus, Ommatius, Maira, Psilopus etc., must be left to the mo- 

 nographer. M.^ van der Wulp has made an excellent beginning 

 with his monograph of the Asilidae of the Archipelago. And 

 the opportunities for such monographic treatment would become 

 more frequent, if the public museums, imitating the noble example 

 of the Museo Civico of Genoa, adopted a more liberal policy in 

 communicating their materials to the would-be monographer. 

 Such lists as the present would, in such a case serve to show, 

 where the materials are to be found. 



In concluding, I take pleasure to express my sincere gratitude 

 to the authorities of the British Museum and of the Zoological 

 Museums in Vienna and Leiden , and also to M.' v. d. Wulp , 

 at the Hague for the facilities which they have offered me du- 

 ring tlie preparation of this work. I am greatly indebted to 

 D.^ Gestro, Vice Director of the Museo Civico, for his unfailing 

 kindness and assistance. The admirable order in which I received 

 the collections, especially as to the labeling with localities and 

 dates, has greatly facilitated the progress of my work. 



Florence, Novemb. 1880. 



Ch. R. OsTEN Sacken. 



(') The extent to which this last statement is true will become clear to those who 

 will take the trouble to read the Preface to my: Catalogue of the described Dip- 

 tera of North-America, second edition, Washington 1S7S. 



