NEUROTERUS OSTREUS. 123 
three months. The imagines appear earlier than those 
of any leaf gall. 
This small, but strikingly beautiful, and unique 
shaped gall, excites admiration on account of its 
attractive appearance, and also because of the enor- 
mous numbers so frequently to be seen on a leaf. 
Probably there is no other gall so numerous within any 
given area as this species. 
In the summer and autumn of 1904 oak galls were 
unusually abundant, and those of M. numismutis 
appeared to exceed all other kinds. Mr. E. W. Swan- 
ton, of the Educational Museum at Haslemere, kindly 
communicated to me that he “ picked three leaves (of 
Q. pedunculata), at random from an oak branch, the 
leaves of which were plentifully sprinkled with the 
silk-button gall, and carefully counted the galls upon 
them. On the first were 502, the second 558, the 
third 681; a total of 1741 galls—an average of 580 for 
each leaf.’ I noticed the same phenomenon in several 
parts of Sussex during the same autumn, and have in 
my own collection leaves bearing similar numbers. 
The gall is small and requires the aid of a lens to 
discern the peculiarities of its structure. It appears 
as a small flat disc attached by an extremely short 
pedicle, grows rapidly, and varies much in size. 
Ultimately it becomes circular in outline, flat next to 
the leaf, and hemispherical in shape. A circular 
depression at the top occupies rather more than one- 
third of its total diameter. 
All the lentiform galls appear to have been observed 
in England by Dr. Sir Thomas Browne, and mentioned 
by him in correspondence with Dr. Merrett in 1668. 
Neuroterus ostreus, Hartig. 
(Plate L.) 
Neuroterus ostreus, Giraud, Mayr, Miller, Fitch, Adler; Andricus 
ostreus, Mayr, Cameron. 
