160 C. H. T. TOWNSEND, 



Western Diptera, Osten Sacken recoi'ds two cases of Systropus being 

 bred from larv?e of Limacodes. Doubtless all the species of Systro- 

 jnis mimic more or less closely some species of aculeata hymenop- 

 tera, as does the present certain species of Ammopldla. Certainly 

 the close imitation of Aimiiophila by the [)resent species must mean 

 something, either that the Systropus is parasitic in its larval state in 

 Ammophila (larva, pupa or adult*, or possibly that it is parasitic in 

 some of the larvse with which Ammophila stores its nests. The lat- 

 ter supposition would explaiu the above records by Osten Sacken of 

 its parasitism of Limacodes. The long hind legs are an important 

 part in the mimicry. The Systropus allows them to hang down when 

 flying, just as does Ammophila. 



The American species oi' Systropus so far known are divisible into 

 two groups, corresponding apparently to the temperate and tropical 

 faunal regions, the temperate group characterized by the abdomen 

 being black at both ends and red in the middle, the five species of 

 whi(:;h are all from the United States ; the other characterized by 

 the abdomen not being so colored, the ten species of which occur 

 collectively from Mexico to Brazil. For a synoptic table of the 

 neotropical species, see Osten Sacken, Biologia C. A. Dipt. 1, p. 157, 

 where this division of groups is adopted. The following table will 

 separate the U. S. species, but it also, like Osten Sacken's, is made 

 from descriptions and must be used with caution : 



Thorax with humeral spots ; abdomen red except base and tip 2. 



Thorax without humeral spots; abdomen black with red in middle and of less 

 extent 4. 



2. Humeral spots white; front coxae red, middle ones red and black. 



' ' . i*"'- ■; iiiacer Loew. 

 Humeral spots red or yellow, all the coxae black 3. 



3. Legs extirely black, humeral spots red like abdomen, wings with only the 



veins infuscate, third antenual joint not twice as long as second. 



augiilatii*« Karsch. 



Front and middle tibiae and metatarsi striate with white and yellow pubescent 



lines, humeral spots bright yellow, strongly contrasted with color of 



abdomen; wings distinctly infuscate with costal portion more deeply 



so ; third antennal joint between 2 and 3 times as long as second. 



aiiiiiiopliiloidcs n. sp. 



4. Legs wholly black i ii I iiscat ii!!t Karsch. 



Legs striate, with yellow anteriorly iiiibecilliis Karsch. 



Volucella opalesceiiis n. sp. 



One female, La Cueva (Riley's Ranch), Organ Mts., September 

 4th, in flowers of Datura meteloides before sunrise. Differs from 



