1905.] 239 



ON THE BRITISH SPECIES OP HYDROTMA, Dsv. 

 BY PERCY 11. GRIMSIIAW, F.E.S. 



During the past few months I have made a detailed study of the 

 genus Hydrofcea, with the double object of ascertaining what species 

 undoubtedly occur in our islands, and of writing full and original 

 descriptions of such species, paying especial attention to the chsetotaxy 

 of the legs, a subject which has hitherto been much neglected, es- 

 pecially as regards the female sex. At the outset I made an appeal 

 in this and other journals for the loan of material, and was favoured 

 with a most generous response, receiving many hundi'eds of specimens, 

 most of them in beautiful condition. I had thus tlie advantage of 

 examining an unusually complete representation of the genus, and have 

 accordingly prepared a detailed account of our native species, with 

 drawings of the legs in nearly every case. As the length of such a 

 paper, however, would preclude its publication in a monthly magazine, 

 I have deemed it advisable to publish without further delay a short 

 preliminary account of the genus, limiting myself to the essential 

 characters only of each species, and reserving the fuller details for 

 some later publication, which may possibly take book form. 



Throughout the work I have been largely dependent upon the 

 very valuable Monograph published by Herr P. Stein in 1903, entitled 

 " Die europaischen Arten der Gattung HydrotcBa, Rob.-Desv." (Ver- 

 handl. der k. k. zool.-bot. Ges. Wien, 1903, pp. 285-337), and although 

 all the descriptions I have written (with the exception of the females 

 of three species) are original and drawn up from specimens actually 

 examined by me, yet in the construction of the keys and in the identi- 

 fication of doubtful specimens I have derived invaluable hints from 

 Herr Stein's paper. At the same time I have described the females 

 of three species which were previously unknown, while that of one 

 species (if. cinerea, Dsv.) has yet to be discovered. 



In the description of the leg-bristles I have followed the system 

 introduced by me in the present Magazine (1905, pp. 173-176), and 

 have paid moi'e attention to such bristles than perhaps other writers, 

 believing as I do that fairly easy and reliable characters can be 

 founded upon them, especially in the case of the female sex, where 

 identification in the AntJiomyiidce is usually a matter of some difiiculty. 



It now remains for me to express my great indebtedness to the 

 gentlemen who have favoured me with the loan of specimens. Mr. 

 E. E. Austen, of the British Museum, very kindly entrusted me with 

 the examination of the specimens under his charge ; the Eev. E. N. 



V 2 



