NEIIKOTEEUS OSTEEUS. 123 



three months. The imagines apjDear earlier than those 

 of any leaf gall. 



This small, l^ut 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 1 904 oak galls were 

 unusually al^undant, and those of N. numismatis 

 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. pedunciilafn), 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 17-tl galls — an average of 580 for 

 each leaf." I noticed the same phenomenon in several 

 parts of Sussex dui'ing 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, Griraiicl, Mayr, Miiller, Fitch, Adler ; Andricus 

 ostreus, Mayr, Cameron. 



