98 DIPTERA OF NORTH AMERICA. [PART IV. 



the British Museum, numerous specimens of Trochobola from 

 New Holland, Yan Diemen's Land, and New Zealand, showing 

 that they are quite common there ; one of them, marked Limnobia 

 tessellata White, which I examined, showed precisely the same 

 distribution of the spots on the wings as T. imperialis or argus ; 

 I did not notice, however, whether the other specimens belonged 

 to the same species or not. 



In the Proc. Philad. Entomol. Soc. 1865, p. 226, I had pro- 

 posed for this group the name of Discobola, which, being pre- 

 occupied, is replaced here by Trochobola (from rpoxoj, a wheel, 

 and /3aM.co, I throw). 



1. T. argus Say. % and £ • — Fuscano-flavida ; alis fusco ocellatis. 



Brownish-yellow, wings witli ocellate brown spots (Tab. I, fig. 4). Long, 

 corp. 0.25—0.3. 



Syn. Limnobia argus Say, Long's Exped. Append, p. 358. — Wiedemann, 

 Auss. Zw. I, p. 33, 17.— 0.. Sacken, Proc. Ac. Nat. Sc. Phil. 

 1859 2 p. 217. 



Head, rostrum, palpi, and antennae black; thorax yellowish 

 with three brown stripes above ; the intermediate double ; pleurae 

 with two brown stripes ; halteres with a brown band across the 

 stem; knob likewise brown; abdomen brownish, genitals paler; 

 feet yellowish ; femora with a brown band at some distance from 

 the tip ; tip of the tibiae and last joints of the tarsi infuscated. 

 Wings yellowish or whitish, with brown, ocellate spots especially 

 along the anterior and posterior margins ; the centre of these 

 spots, forming the pupil of the eye, is likewise infuscated ; these 

 centres are mostly placed at the origin or at the tip of the longi- 

 tudinal veins, or upon cross-veins : thus a complete ocellus has 

 the origin of the praefurca for its centre ; a double one surrounds, 

 as centres, the inner end of the submarginal cell and the small 

 cross-vein ; other centres of less complete ocelli are the tip of 

 the seventh longitudinal vein and the supernumerary cross-vein, 

 existing there ; likewise the tip of the sixth vein and the inner end 

 of the fifth basal cell ; the apical portion of the wing contains 

 several more ocelli, more or less distinctly marked in different 

 specimens and giving that portion of the wing a variegated 

 appearance. 



Eab. Northwestern Territory (Say) ; Nova Scotia (British 



