GALL MITES. 365 



CASE of which the larvse break down the hairy covering of the leaves, 



XVII. V o y 



and the cells become yellow and scarred through the sucking out 

 cf the leaves. 



On the Elm. 



Phytoptus, Sp. 



G. V. Frauenfeld (" Verh. and zool. bot. Ges. Wien., 1865, 

 p. 897 ") without indicating where it was found, described small 

 green, very solid leaf-galls, which stand out like pegs on the upper 

 and under side of the leaves. Very often they are found singly 

 on the first leaf of the shoot, most numerously on the second and 

 third leaves. 



Phytoptus, Sp. 



Globular purse-shaped galls, pale green in colour, with rather 

 coarse hairs, and very thin walls from i^ to 2 millimetres in thick- 

 ness. They are scattered often in great numbers over the upper 

 side of the leaf. The walls are so thin, that the slightest touch 

 leaves an impression, and they can best be compared to a bubble 

 that has not been completely blown. The inside is bare and 

 shining. The entrance to the gall on the under side projects 

 scarcely or not at all beyond the surface of the leaf, and is closed 

 by a loose white Erineum, which is also continued in the gall 

 stalks. The small number of gall mites in it are light brown. 

 This Acarocecidium is occasionally found on the first, but, as a 

 rule, principally on the second leaf of the shoot. 



On the Alder. 

 Erineum alneum, Pers. 

 Most frequent on the under side, very seldom on the upper side 

 of the leaf. The gall mite living in it is transparent white. 



Cephaloneon pustulatum, Bremi, 

 Upon the upper side of the leaf. In spring, shortly after the 



