218 Mr. A. H. Haliday on the generic distributimi 



It is remarkable, that R. Desvoidy, who was not likely to be 

 influenced by too much deference for the authority of his pre- 

 decessors, has also placed with his Hydrellidece a group of 

 Cordyluroi less aberrant (than C. livens) from the ordinary cha- 

 racter; the type of his genus Nupharia being the C.fraterna 

 of Meigen. In other respects his method to some extent cor- 

 roborates the distinction of this tribe, as his seventh family 

 Napceellce comprises, in addition to Fallen^s Hydromyzidce, 

 only the Sphceroceridce and some osculant species allied to 

 these last, and is again divided into two groups. It is true, 

 that he has drawn the hne of separation between these so as 

 to include in the latter the genus Ephydra of Fallen, disjoined 

 from its more natural affinities — the remainder of the Hydro- 

 myzidce constituting his first tribe Hydrellidece, The origin 

 of this discrepancy is to be sought in the principles of Des- 

 voidy's system, which give a preference to partial knowledge 

 or conjecture concerning habits and economy, as the basis of 

 arrangement, over the study of (at least external) structure; 

 with the exception of this particular, and of his habitual dis- 

 regard of the labours of previous writers, this portion of 

 Desvoidy^s Essay is executed with judgement and precision, 

 and as a generic arrangement of this tribe is second only to 

 Fallen's. Macquart, remanding Hydromyza and Nupharia to 

 their proper place among the Cordylurce^ has further limited 

 the Hydromyzidce, by rejecting all the species which have not 

 the arista pectinate. These he has placed in his family Pio- 

 philidce, in conjunction with many genera of diversified cha- 

 racter and remote affinity. 



I here employ the tribe as defined by Fallen in his ^ Diptera 

 Sueciae,' removing Hydromyza to the Scatomyzidce, and re- 

 jecting the addition of Ropalomera. The tribe thus limited 

 is one of the most remote from the Calyptrate section, and 

 can scarcely be confounded with any other group, unless it be 

 with certain species of the Geomyzidce, which appear to offer 

 the nearest affinity. Nevertheless from these the Hydromy- 

 zidce may be distinguished, either by the form of the head and 

 mouth, the characteristic imperfection of the cells of the wing, 

 or the total concealment of the ovipositor. The greater num- 

 ber frequent the neighbourhood of waters, a destination indi- 



