388 ON THE INSECTS FROM XEAV BRITAIN. 



slightly beyond the tips of the ehi:ra. Only one specimen was found. The occurrence 

 of this remarkable genus in New Britain or the Duke of York island has not been 

 previously noticed. 



Order Hymenoptera. 



New Britain is evidently rich in Hymenoptera, as the small number of examples 

 obtained by Dr Willey consists of comparatively many species. They belong chiefly to the 

 Aculeata. I have not ventured to describe any of them except a species of Thynnus 

 that possesses a peculiar abdominal structure. I may however allude to an abeiTation of 

 instinct observed by Dr Willey in the case of a wasp of the genus Polistes (probabh- an 

 undescribed species allied to P. colonicus). Instead of one egg being placed in each cell, 

 there are several, as shown in Fig. 14, PI. XXXV., which represents five cells of the 

 nest of the insect in question. The cell on the left, below, is closed for the purpose of 

 pupation, and the one above it is empty. The three cells to the right contain, respec- 

 tively, one .5, one 3, eggs, and the other (the one to the right) 2 just-hatched larvae. 

 Notwithstanding the supernumerary eggs, only one larva in each cell attains maturity, 

 though how the others are disposed of we do not know, Dr Willey ha^"ing made no 

 observations on this point. Neither did he ascertain whether this aberration is com- 

 mon in the species, or confined to this nest. He brought back the nest of a second, 

 and smaller, species of Polistes (also probably undescribed), and in this case there is 

 only one egg in each cell, as one would e.xpect. It does not seem possible to account 

 for so striking an aberration of instinct as this, by supposing that there were more 

 eggs produced than cells to place them in, because several of the cells in the nest 

 are quite empty. 



Family APIDAE. 



KOPTORTHOSOMA sp. 



Koptorthosoma sp. atF. K. aestuantis, Perkins, Ent. Mo. Mag., Feb. 1899, p. 38. 



Mr R. C. L. Perkins has (1. c.) called attention to the very extraordinary sym- 

 biosis of female bees of the genus Koptorthosoma and certain Acai'ids ; the bee being 

 provided with a special chamber in the abdomen which is tenanted by the Acari. 

 The males do not possess this structure ; Mr Perkins mentions the remarkable fact 

 that in this species from New Britain the female is destitute of the special chamber, 

 though it exists in the closely allied K. aestuans. Dr Willey only procured two 

 females of this interesting species, and no male. 



Fasiilt THYNNIDAE. 



Thynnus serriger, n. sp. PI. XXXV., Fig. 13, $ ; 13 a, extremity of abdomen. 



$. Nigricans, hie inde pallide setosus; scutello, abdominis maculis lateralibus, 

 fasciaque mediana in medio interrupta, albicantibus. Long. 12 mm. 



