of certain species of Willow. — Part 2nd. 227 



differ but little in Bize, structure or color, some species however being 

 spotted. In a few galls, e. g. Cratsegi vermiculus Walsh MS, which 

 occurs abundantly both on Crataegus tomentosa and Cr. crus-galli, the 

 larvae of the mite are of a pale pink color. 



No. 15. Gall S. 2ENIGMA Walsh. — I have little doubt that this 

 gall also is a deformation produced by an Acarus. From its great 

 scarcity in 1X06. 1 was unable to examine any green specimens, but 

 on Aug. 27 I found among the crumpled exterior surface of a partly 

 dried-up specimen a half-grown Acarus similar to those found in S. 

 si men. It may be stated that on the tree from which this gall was 

 procured there were no S. semen galls ; for this gall too, as well as S. 

 senigma, though so exorbitantly abundant in 186-4 has been compara- 

 tively quite scarce in 1866. Usually in Acaridous galls the larvae live 

 in a hollow inside; but in one on the leaf-stalk of the Black Walnut 

 — Juglandis cau/is Walsh MS — they reside among the brown external 

 woolly pubescence, just as in S. senigma they probably reside in the 

 crumpled external surface of that gall. The Cecidomyidous larva) 

 that I found in June and August in S. senigma were most likely in- 

 quilines. (Proc. etc. III. pp. .608 — 9.) I have received through Mr. 

 Bebb from Cr. W. Clinton, Esq., Buffalo, N. Y., pressed specimens of 

 this gall growing on the same Willow — S. nigra — on which I find it 

 exclusively. Hence there are at least 3 W T illow-galls common to the 

 Eastern and the Western States — $. strobiluidcs, S. siliqua, and *S'. 

 senigma. 



IXQUILINES OR GUEST-FLIES. 

 • Genus CECIDOMYIA, Subgenus CECIDOMYIA. 



A. Cecidomyia albovittata Walsh. On May 5 I bred a $ 

 from the gall S. strobiliscus Walsh found on S. discolor. 



D. Cecidomyia orbitalis Walsh. One % , one 9, which may 

 possibly belong to this species, and which must have come out since 

 May 14, were found May 26 dead and dry in a jar containing many 

 of the Tenthredinidous galls S. gemma n. sp. They are a little 

 smaller than my smallest orbitalis, and the % has 17-jointed, not 18 

 — 19-jointed antennae, with the pedicels on their basal -, about as long 

 as the globular part of each joint; otherwise, so far as can well be 

 ascertained from the dried specimens, they do not differ materially, 

 though I incline to believe them distinct from the difference in their 

 pedicels. 



Genus CECIDOMYIA. Subgenus DIPLOSIS. 



D. DlPLOSIS atroctlaris Walsh. — I bred a single % Sept. 27th 



