from the Rio Nautla^ State of Vera Cruz. 273 



find to vary greatly, being nearly or quite obsolete in some 

 males. 'I'lie supposed cliaracteristic black on tip of the 

 female abdonn'ii is often subobsDlete or wholly wanting. 



kSize is another character that cannot be relied uj)on in 

 this group, which seems to approach the nearly allied family 

 Conopidse in this respect. In some species of Zodion, for 

 examj)le, the disparity in size is sometimes very great. I 

 have two specimens of the same sex (mah;) of Z. splendeyis, 

 one of which is at least five times as large, bulk for bulk, as 

 the other, and yet does not diftcr appreciably otherwise (see 

 forthcoming papers on Diptera of the Organ Mountains and 

 Diptera of the Mesilla Valley, N.M.). 



The scutellum is often subtranslucent, more or less pol- 

 linose, so as to appear nearly concolorous with the yellow or 

 reddish abdomen in species with such colours prevailing, 

 rather than with the thorax. This character cannot be 

 trusted, as it is changeable in the same specimen, according 

 to age, degree of preservation, &c. Moreover, there are all 

 gradations in specimens in this respect, so that no separation 

 can be made. 



The form of the abdomen is not always constant as a 

 sexual character. Females of the smaller forms often ap- 

 proach the male in the wider subflattened abdomen, while 

 some males even boast the subcylindric abdomen of the 

 female. In all cases of doubt as to sex, the only criterion to 

 be depended upon lies in the sexual organs themselves. 



The forms of Trichopoda exhibit such a range in size, 

 coloration of wings, abdomen, &c., that it is likely that many 

 of the older names will have to be classed as synonyms, or 

 continued only to mark varieties. The above remarks on 

 colour variation apply more particularly to the smaller forms, 

 pennipes and var. pilipes. 



'I'he following table of species and varieties of Trichopoda 

 includes only the forms, and sexes of those forms, known to 

 me from examination : — 



Table of Species of Trichopoda. 



Males. 



1 . Wings with only a narrow internal border, 



hyaline 5. 



"Wings with at most the costal half coloured, 

 the inner half or more clear 2. 



2. Abdomen black, with a large pale yellow 



spot on each side at base j)hasi(ma, sp, n. 



Abdomen brown or black, without such 

 spots, golden poUiuose on apical segments. 3. 



