756 BULLETIN UNITED STATES GEOLOGICAL SURVEY. 



Family Syephid^e. 



Eristalis lapideus. — A poorly preserved specimen, showing little that 

 is characteristic, but which belongs near Eristalis or Helophilus. The 

 body is preserved on a dorsal aspect, with wings partially expanded; 

 the head is nearly wanting, the thorax without markings. The wings 

 are distinct only on the basal half, and even here show no neuration at 

 all beyond the general course of the principal veins at the very base ; 

 the alulse, however, are very distinct, very large, their breadth (along 

 the wing) fully equal to half the breadth of the thorax, dark, with ob- 

 liquely transverse dark ridges, indicating that they were wrinkled in 

 nature, much as in Volucella or Oestrus. Abdomen long, broadest in the 

 middle of the basal half, beyond tapering considerably, the tip roundly 

 pointed ; apical half of basal joint black, forming a distinct transverse 

 straight band ; the number of abdominal joints appears to be five. 

 Length of thorax 3.5'"'"; breadth of same 3.25"""; length of abdomen 

 6.5'"'"; wings 12'"'"; breadth of same 3.5""". Chagrin Yalley. 



-Family Muscid^e. 



There are five species of Dipterous larvse in the collection, all belong- 

 ing to the Muscid(v, and representing at least two very different groups, 

 each of which has more than one representative. 



Musca ascarides. — First there is a species to which a considerable 

 number of specimens belong, which may take the name here given. 

 Some of the specimens are comi)lete ; others consist of emptied skins 

 only. When contracted, the body is thick, especially on the anterior 

 half, and about twice as long as broad, closely resembling the larva 

 of a bot-fly. Both extremities are rounded, the anterior very broadly, 

 while the i:)osterior half tapers very regularly. In one specimen, 

 which is not so much shrunken, the body is fusiform, and about three 

 and a half times longer than broad; the head and hinder extremity 

 tapering in a nearly equal degree. In the emptied skins, as in the 

 others, it may be seen that the normal form is a blunt, squarely rounded 

 head, behind w^hich the body is nearly equal, and then tapers toward 

 the tail. At the anterior extremity may be nearly always seen a por- 

 tion of the mandibles, consisting of a pair of very slender rods or 

 blades converging anteriorly and terminating in two attingent rounded 

 lobes, attached to the inner edge of the blades. The anterior spiracles 

 are seen in a single specimen as a simple, rounded, dark sjDot just out- 

 side the middle of either lateral half; the two lateral tracheal ves'iols 

 may be seen in nearly all the specimens, and especially at the hinder 

 extremity, and fragments of them are frequently scattered about on the 

 stones; they are very large. The integument is generall}^ rather dark, 

 and more or less blotched, and covered profusely and almost uniformly 

 with backwaxd-directed hairs ; these are short, tapering, and mod- 

 erately stout, though minute. Length of contracted bodies 11.5'"'"; 



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