Insects. 



6105 



slndy of these curious little atoms more intelligible to a beginner, 

 and of avoiding the confusion which now exists from the indiscrimi- 

 nate application of the same name to species widely differing from 

 each other. For this purpose I have, to the utmost of my power, 

 carefully compared the descriptions given by most of the authors 

 referred to in the list with specimens of each species, and in many 

 cases 1 have received the valuable assistance of my friend Mr. Water- 

 house, who has with much kindness examined those works to which I 

 had not the means of access. 



I have made some alterations in the disposition of the genera, since 

 it appears to me that this family is closely allied to the Brachelytra, 

 not only in the external form and habits of the species, but especially 

 in the dissections of the mouth, and that, in a general arrangement of 

 the order, it should follow that extensive class. According. to this 

 idea the transition through Ptinella to the typical genus Trichopteryx 

 is easy and natural, and, however impracticable as a whole a purely 

 natural arrangement may be, I do not think it should be entirely lost 

 sight of; and again, by placing Ptilium, Ptenidium and Nossidium 

 at the end of the family, you leave this group, by an easy descent, 

 either to Scaphidium or Choleva, to which in many points they bear 

 an evident affinity. 



With regard to the separation of Ptinella and some others from the 

 genera with which they have been hitherto associated, I conceive that 

 I am justified in thus dividing them by their great external dissimi- 

 larity ; and where external characters are the almost only available 

 points of distinction, they carry with them a weight which they would 

 not otherwise possess. I much regret that, owing to the extreme 

 rarity of many of these species, I have been unable to obtain dis- 

 sections, as I believe that such an examination would fully sanction 

 their separation. In order to avoid multiplying terms, I have adopted 

 for these genera names previously used in the same family by Mots- 

 choulsky and other writers ; but as these names were not in every 

 case originally applied to the species to which I have assigned them, 

 I subjoin descriptions of the genera and species now characterized 

 for the first time. 



I have, for the same reason, retained the name of Ptilium for the 

 genus to which Erichson assigned it, as he appears to have been the 

 first to publish its characters : all reference to Gyllenhal must how- 

 ever be expunged, as that author not only did not intend the name 

 for any of the species to which it is now given, but actually assigns 

 it to two species of Ptenidium, viz, pusillum and punctatum. 



XVI. 2 K 



