habits of certain species of Euriitomides. 325 



Another species of Isosoma, the antennae of which 

 exactly agree with those of I. orchidearnm, was reared by 

 Mr. Whitmarsh from hard hollow pink pepper-corn galls 

 on the under side of oak-leaves gathered in August, 1872, 

 the flies immediately making their exit from the galls. 

 The microscopical preparations made of this species by 

 Mr. Whitmarsh exhibit several parts of its structure so 

 clearly that I have thought it desirable to represent 

 them, as the species which attacks the Cattleyia buds will 

 doubtless possess a perfectly similar organisation. 



The mandibles (PI. xiv., fig. 15a) are very robust, 

 subtriangular, pointed at the tip with one acute and one 

 broad truncated tooth on the inner edge. The lower 

 parts of the mouth are well defined. The maxillae (fig. 

 15) have a broad basal portion working upon a narrow 

 muscular attachment ; whilst the apical portion is formed 

 of two blades, slightly curved, obtuse at the tips, setose 

 on the outer margin ; and the maxillary palpi are dis- 

 tinctly 4-jointed, the three basal joints small, nearly 

 equal in size (the 2nd being rather larger than the 

 others) ; and the 4th is as long as the rest united, and 

 slightly dilated and obliquely truncated at the tip.* The 

 mentum is semiovate, the anterior portion being nar- 

 rowed on either side ; it is affixed upon a narrow, 

 elongated triangular stipes ; the labium is as long as the 

 mentum, rounded at its extremity, and the labial palpi 

 are distinctly 3-jointed, the basal joint being the thickest, 

 the 2nd joint the shortest, and the 3rd slender, obtuse, 

 and setose at the tip. The body of the male is terminated 

 by a retractile flattened elongated penis, pointed at its 

 extremity (fig. 17), and is furnished with a pair of short 

 flattened claspers, each having three short acute teeth 

 on its outer apical portion, similar in position and shape 

 to the organs in the males of Sijcophaga crassipes (see 

 Plate iii., figs. 15 to 18). The organs of oviposition in 

 the female are represented in fig. 16, in which the sheath 



* Mr. Curtis, 'Brit. Entom.,' pi. 345 (February, 1831), represents 

 the structural details of Decatoma biguttata, Sweclerus, figuring 

 the maxillary palpi as 3-joiuted and the labial palpi as '2-jointed. 

 He states, however, that Mr. HaUday had observed that the 

 maxillary palpi of iJ. longula, Dalman? are 4-jointed, whilst the 

 labial are 2-iointed. In a specimen of, I believe, E. [Decatoma) 

 biguttata, reared from soft cherry-hke galls on the under side of 

 oak-leaves by Mr. Whitmarsh and prepared in Canada balsam, the 

 maxillary palpi are distinctly 4-jointed. 



