300 DIPTERA OF NORTH AMERICA. [PART IV. 



terior ; small cross-vein short ; discal cell rather large, elongated ; 

 its inner end pointed and nearer to the basis of the wing than 

 the inner end of the submarginal cell ; the posterior end of the 

 discal cell emits four veins towards the margin ; the anterior 

 among these veins is very arcuated at its basis, so that the cell it 

 forms seems to be carved out of the first posterior cell ; great 

 cross-vein somewhat beyond the basis, but before the middle of 

 the discal cell ; fifth longitudinal vein incurved at the tip (more 

 structural details about this species have been given among the 

 generic characters). 



Hob. White Mountains, N. H., end of June, 1864; two male 

 specimens. 



Observation I. I have not seen the female of this species, but 

 I suppose that its antennas are a little shorter and its wings some- 

 what smaller ; at least these characters distinguish the female of 

 C. distinctissima. I suppose also that in the American species, 

 as in the European, the venation may be somewhat variable, and 

 that in some cases the second posterior cell may be petiolate, 

 instead of sessile. 



Observation II. I will mention here some peculiarities of the 

 suture of the thorax of this species, which I have omitted in 

 its description, as unimportant for its recognition. The thoracic 

 transverse suture is marked by a very delicate groove in the 

 shape of a Y or of a fork, the two ends of which run parallel 

 towards the collare, and the handle reaches the scutellum ; a 

 transverse impression on each side connects this fork with the 

 sides of the thorax, near the root of the wings, and thus com- 

 pletes the transverse suture. These slender grooves on the 

 thoracic dorsum foreshadow the more distinct sculpture of Tri- 

 ogma. The scutellum in both genera has two distinct pits near 

 its basis. 



Observation III. The European 0. distinctissima is almost 

 identical with C. americana. The three specimens of the former, 

 which I can compare, show the following differences : the dark 

 spot on the head and the stripes of the thorax are not brown, but 

 of an opaque black ; there is a black spot, divided in two parts by 

 a fine longitudinal yellow line, on the posterior part of the meta- 

 thorax (there is no vestige of such a spot in C. americana) ; the 

 feet are also of a darker coloring, and the tips of the femora and of 

 the tibiae are distinctly infuscated; the wings have a more distinct 



