Banks, Greene, McAtee, and Shannon — Dist. of Col. Diptera. 175 



Washington is no exception. For example, Xylota marginalis 

 is of such a distinctly northern distribution, its capture here 

 was a great surprise; similarly Volucella vesiculosa, V. obesa, and 

 Meromacrus cruciger are so characteristically southern that none 

 would expect them here; likewise Eristalis latifrons and Platy- 

 chirus chaetopodius are typical of western conditions. 



However, there are cases in which of two closely allied forms 

 occurring in the north, only one is found here. For example, 

 Eristalis meigenii and E. arbustorum are closely related and occur 

 together in various parts of the north ; nevertheless all speci- 

 mens we take here (and commonly) are E. arbustorum ; Helo- 

 philus latifrons and H. similis present another case; all we get 

 here (and also commonly) are H. similis. Yet from the known 

 distribution one would expect both species here. There are 

 evidently laws of distribution ; but distribution depends on such 

 a complicated set of conditions, even outside of temperature and 

 moisture, that we can not with present knowledge predict 

 occurrence. 



The total number of species in the present list is 136. There 

 are also 2 named varieties. Of this number three, namely, 

 Paragus dimidiatus, Xanthogramma divisa, and Helophilus divisus, 

 are of uncertain specific standing; two, Sphegina campannlata 

 and Helophilus lunulatus, are not certainly identified (although 

 the latter, whatever its identity, is additional to the other species 

 of the genus listed) ; and one, Merodon equestris, does not have 

 an absolutely clear title to a place in the list. The net total of 

 species may therefore be placed at about 131. For comparison 

 it may be stated that the number of species of Syrphidse listed 

 for New Jersey* is 132, with 2 named varieties. The latter list 

 contains two synonyms, namely, Chilosia tristis and Xylota 

 tuberans (perhaps Helophilus divisus should be added), so that 

 the net total is about 130. 



Members of the Washington Biologists' Field Club have 

 planned and have in part accomplished the cataloging of the 

 fauna of Plummers Island, Md., the home of the club. The 

 present list obviates the need of a publication on the Syrphidae. 

 Seventy of the species herein cataloged have been taken upon 

 Plummers Island. The records quoted indicate which species 



•Johnson, C. W. in "The Insects of New Jersey," Ann. Rep. N. J. State Museum, 

 1909 (1910), pp. 762-771. 



