XVI PREFACE. 



collcctifon into his own , without quite finishing this operation. 

 Dr. Hagen , who saw both collections at that time (in 1839), 

 speaks of them as being united; („einverleibt" ; see Stett. 

 Ent. Zeitschr. 1844, p. 131). Under such circumstances, the 

 study of these types requires some critical acumen, and a con- 

 stant reference to both collections; but when attention is paid 

 to Wiedemann's handwriting, to his statements about the number, 

 the sex and the condition of the described specimens, and finally 

 to the square, red labels, with which the types, thus transferred 

 to V. "W'inthem's collection are marked, but little difficulty will 

 be experienced in finding out the true typical specimens. 



Mr. Macquart's types are chiefly preserved in the Museum 

 in Lille, in that of the Jardin des Plantes in Paris, and in the 

 collection of Mr. Bigot, in the same city; the latter collection 

 also contains the diptera which Macquart had described from 

 Mr. Serville's collection. Many types, principally those of the 

 descriptions in the Histoire Katurelle des Dipteres, I did not 

 find in the above-named collections; they are very probably 

 lost. And as many of the descriptions in that work are too 

 short to be intelligible, they will have to be canceled. I even 

 suspect that several of the species, described there as North 

 American, and which it has not been possible to identify since, 

 belong to other countries. One instance of that kind , (Ptilogyna 

 fuliginosa, an australian species), I have traced with certainty. 



The types of Mr. Walker's descriptions (including those in 

 in the Dtpicra Saunclersiana) are preserved in the British 

 Museum. 



Mr. Walker's writings on the order of Diptera are not 

 better than his publications on Lepidoptera, Hemiptcra and 

 Orthoptera, as characterized by other authors. The same species 

 arn often found described under several different specific names 

 and placed in different genera ; well characterized species of a certain 

 genus are placed in the wrong, sometimes in very distant, genera, 

 or even in the wrong family. In the great majority of cases 

 the descriptions of new species were drawn from a single, often 

 hardly recognizable specimen; and when new species happen to 

 be represented by more than one type-specimen, these are almost 



