564< Modem Nomenclature of Natural History. 



value of the two kinds of groups : neither will I here enter 

 into any attempt to show the impropriety of the practice, 

 adopted by some authors, of employing the old generic name 

 for the most common species of the genus ; a practice which 

 must be considered exceedingly vague and indefinite. 



I have elsewhere endeavoured to show the advantages likely 

 to result from the uniform practice of considering, as entitled 

 to the original generic name, that particular species which, 

 from having been placed at the head of a genus, we cannot but 

 suppose was considered by its founder as more especially pos- 

 sessing the generic character of the group ; or that which, in 

 many instances, is expressly stated to have been employed as 

 such type. In this enquiry, moreover, I think that we are 

 bound to resort, on all occasions, to the original establishment 

 of the genus, notwithstanding the modifications which it may 

 have subsequently undergone, even at the hands of its original 

 founder. This principle I would, at all events, more parti- 

 cularly insist upon in groups where the generic and subgeneric 

 synonymy is in a state of confusion. Perhaps the more effec- 

 tual manner of pointing out the necessity of the adoption of 

 the above-mentioned principle will be, to show the confusion 

 which has originated in consequence of its non-adoption : this 

 I will do as shortly as possible. 



The dipterous genus Xylota was separated by Meigen from 

 the great genus Syrphus, the ikfusca pipiens of Linnaeus 

 being placed as the first species, forming, in fact, the first sec- 

 tion. On minutely investigating the genus, this species was 

 found to possess characters to warrant its establishment by St. 

 Fargeau and Serville (who have been followed by Mr. Curtis) as 

 a separate subgenus. Instead, however, of retaining the name 

 Xylota for the Musca pipiens, it has been improperly, as it 

 seems to me, conferred upon the other species ; whilst the real 

 type of Xylota has been termed by them Syritta. In Mr. 

 Stephens's catalogue the name Xylota is correctly applied 

 to M. pipiens, the remainder of the species being placed in 

 a distinct, although unnamed, genus ; and for which (as it 

 will be improper to employ Syritta otherwise than as a syno- 

 nyme for the true Xylota) a new generic name must be still 

 proposed. 



In like manner, the confusion which has arisen in the ge- 

 neric, or rather subgeneric, nomenclature of the various sections 

 of the Tachydromidae is very perplexing, and would occupy 

 too much time at present to unravel. The same observation 

 may be likewise applied to numerous other groups. The 

 only other instance which I shall therefore notice is, the genus 

 Pemphredon of Latreille, one of the sections of which has 



