DIPTERA. G29 



gradually widened behind, with small points on tlie sides, and terminated by six filaments. It is furnished beneath 

 with two spiracles and six fleshy lobes, each armed with three long- hooks. 



Sericomt/ia, Mei|i;., has the third joint of the antenna; semiorbicular. 



EristaUs, Meig-., restricted to the species which have the seta villose, and which differ from Volucella in the 

 wings, which have the outer cell closed by the posterior edge of the wing. 



Others differ from the preceding by having the seta of the antennae simple, or without distinct hairs ; the body 

 short, and the abdomen triangular. 



The two following subgenera have the last outer cell of the wings strongly sinuated on the outer edge, and the 

 body is generally hairy. 



Malluta, Meig., has the last joint of the antenna; transversely trapeziform. 



Helop/iilus, Meig., has the same joint of a semi-oval form ; the body less hairy than in the preceding. The 

 larvae of many have the body terminated by a long tail, which they can elongate and elevate perpendicularly until 

 it reaches the surface of the water or cloaca in which they reside, in order to respire by means of the aperture at 

 its extremity. Their interior presents two large and very brilliant trachea, wliich, near the tail, are much folded, 

 and kept in constant agitation ; vessels filled with rain-water often contain many of these larvw. Type, Musca tenax, 

 Linn., a very common species, resembling in size and colour the male of the Hive Bee. Its larva is rat-tailed ; and 

 it is said to be so tough, that the strongest pressure will not destroy it. 



Others differ in having the outer cell of the wings closed by the posterior margin of the wing, its outer edge being 

 straight, or but feebly sinuated ; the frontal prominence is very short, and the abdomen narrower than in the pre- 

 ceding. 



Si/rpftus proper, (Scteva, Fabr.), has the abdomen narrowed from the base to the apex. Their larva; feed only 

 upon all kinds of Aphides, which they often hold up in the air, and suck them very quickly ; the body of these 

 larva; is of an elongate-conic form, uneven, and even sometimes spinose. AVhen ready to metamorphose, they fix 

 themselves to leaves or other substances by a glutinous secretion ; the body shortens, and its anterior end, which 

 was the slenderest, becomes the thickest, ^ctcca Ribesii, Fabr., [a very common species]. 



Chrysogaster, Meig., has the forehead of the females channelled on each side ; and the nasal eminence is thicker. 



Baccha, Meig., differs from the last in having the abdomen narrow at the base, and swollen at the tip. I think 

 the Si/rp/ius conopseus [genus Doros], ought to be added to this, although the palette of its antenna; is less 

 orbicular. 



We now pass to other subgenera, agreeing with the preceding in the form of the muzzle, but the antenna; are at 

 least as long as the face. 



Parafftis, Linn., has the antenna; not fixed on a common footstalk, and their length does not exceed that of 

 the head. 



In the five following, they arise from a common elevated footstalk, and are larger than the head. 



.S>//<'co»i//ia, Latr., has the seta lateral, and inserted on the second joint ; the third joint being very short. A 

 species from Carolina. 



Psarus, has the seta inserted on the back of the third joint, near the top ; this joint is nearly oval, of the same 

 length as the second joint; the peduncle of the antenna; is more elevated than in the analogous genera. 



Chrysotoxum, Meig., has the seta inserted on the third joint, near the base ; this joint is the longest, forming a 

 narrow and elongate triangle ; the two others are nearly equally long. 



Ccria, Fabr., has the seta terminal ; the body narrow and elongate, like that of a Wasp ; the second and third 

 joints of the antenna; form a fusiform mass ; the abdomen is long and cylindric. 



Cal/icera, Meig., has the seta terminal, and the body short, broad, and silky. The nasal prominence does not 

 exist in the following subgenera ; the antennal seta is nearly always simple, and the wings incumbent on each 

 other. 



Ceratophya, Wied. (with an unarmed scutellum), and 



Aplirites, Latr. (Microdoii, Meig., with the scutellum armed with two teeth), agree with the last subgenera in the 

 length of the antenna;, close together at the base. In the following, they are shorter than the head ; and the hind 

 logs are often large, especially in one sex. 



Merodon, Meig. (having the abdomen triangular and conical), and 



Ascia, Meig. (with the abdomen narrowed at the base, and clavate), have the palette of the antennae oblong-tri- 

 angular. In the following it is short, or but slightly elongated, sub-orbicular, or sub-ovoid. 



Sphegina, has the abdomen clavate, as in Ascia. In the others, it is triangular, conic, or subcylindrical. 



Some of these have the wings not extending beyond the extremity of the abdomen ; and some have tiie hind 

 thighs thickened, and armed with numerous small spines. 



Eumerus, Meig., to which we add his Xylota, which differs only in having the abdomen narrower, and almost 

 linear, il/. plpiens, Linn. 



Milesia, Latr. (Tropidia, Meig.), has the two h.ind legs much longer than the others, with the thighs much thicker, 

 and armed with a single tooth ; in many, the abdomen is conical. 



I'ipiza, Meig. (and Psilota, Meig.), have the hind legs little longer than the others; the abdomen depressed and 

 semi-elliptic. These Diptera have much affinity with the fiyrphi and C/iiysogasteri. 



Bnwhyojia, HotFrn., differs from all the preceding in the wings extending far beyond the abdomen, [in consequence 

 of the shortness of that part of the body]. They otherwise resemble Milesia, and appear to lead to R/iingia. 



RhiiKjin, Scop., forms the second general division of the Syrp/iies, having the probosc.s longer than the head and 

 thorax, and nearly linear. 



