LETTER OF JUNE 23RD, 1 860. 35 



Sub-Fam. GRACILARIN^. Hind-wings extremely narrow, 



setiform or linear-lanceolate. 



Group I. Gracilarides. Hind-wings with median vein 

 two or three -branched ; cell most frequently open, &c. 

 Group II. Lithocolletides. Hind-wings with median 

 vein always simple ; cell always open. 



These groups are subdivided into subordinate groups by 

 means of the most general characters, and these again into 

 others, until at last they are cut up in small groups of genera, 

 which are distinguished from each other by their special and 

 peculiar characters. Thus those which most nearly approach 

 each other in structure are brought into direct contrast, ex- 

 cept when they happen to be separated by some category 

 having a general significance. You will not approve this 

 arrangement, but I find it is so convenient and serviceable that 

 I cannot but believe it will be valuable and useful to others. 

 In the present state of Lepidopterology the attempt to con- 

 struct a natural system must be purely approximative. I 

 should be glad to submit the entire Synopsis of Genera to your 

 inspection, did it not take up too much space to send in MS. 



I have been greatly disappointed this spring in the failure 

 of some of my most interesting pupse to produce imagos. 

 This was the case with the pupa from the larva which made 

 the peculiar mine in the leaf of Ostrya* sent to you last fall, 

 and the tube-making larvae on the lower surface of the oak 

 leaf. I found however a Butalis larva. It mines the leaves 

 of Aster cordifolia in rather a peculiar manner. The lower 

 surface of the leaf, near the base, is covered with a web con- 

 taining silken tubes, and the larvas open mines connected 

 with these, and they are rarely extended to a greater length 

 than that of the body of the miner. They are easily alarmed 

 and immediately retreat from the mine to the web, where 

 they are almost concealed. 



In November, 1858, I found two cases of, I suppose, 

 Coleophora larvae, spun up on the slots of the window- 



* See p. 27. H. T. S. 

 D2 



