758 BULLETIN UNITED STATES GEOLOGICAL SURVEY. 



the anterior portion into two equal halves of the same width as the 

 blackish band. Length of body23""'^; greatest breadth of sanies'"™; 

 breadth posteriorly 3™™; breadth of skin O-S""""; length of segments 

 on same 4™"' 5 length of mandible blades 3.5™™. Chagrin Valley. 



Musca vinculata. — There is still another species, allied to the last- 

 mentioned, which may bear the fiame here proposed. It is represented 

 only by part of emptied skins, all lying on the same stone, and which 

 differ from the preceding species in being absolutely devoid of any hairs? 

 and in having different and much fainter markings. The general color 

 of the. best-preserved specimen is a pale brown, and the markings are 

 scarcely darker transverse bauds, narrowing on the sides, but occupying 

 nearly the entire length of a segment dorsally, and broken into equal 

 parts by two transverse rows of 'very faint and minute pale dots. No 

 specimen is sufficiently perfect to show the shape or the length, but the 

 shape appears to be similar to that of M. hydro^yica, and the insect much 

 smaller than it, for the breadth is 4.5™™, and the length of one segment 

 2™™. Chagrin Valley. 



Nearly all of these species, and especially Musca ascarides, so closely 

 resemble the larva? of bot-flies, that I could scarcely persuade myself 

 that they coul^d not belong to the Oestridce. The appendages of the 

 skin, however, are much more delicate than is usual in Oestndcv, and 

 are uniformly distributed over the surface or are altogether absent. 

 The empty skins, too, have every appearance of belonging to the same 

 insects as the complete bodies, and although these are not cast skins 

 (in which case they would be proved natural inhabitants of the water), 

 for they still contain the harder parts of the internal organs in many 

 cases, but remains of partially decomposed larvce, it would seem impro- 

 bable that so large a number of Oestrid larvse couid be found, when the 

 only way in which they could have reached their present condition would 

 be through the droppings of animals affected by the bots standing in 

 the water. Of course, the reference I have given them is only pro- 

 visional. 



Indeterminate remains of the imagines of three or four species of small 

 Museidcc also occur in the collection from both places. 



Family Helomyzid^. 



Heteromyza detecta.—A single specimen and a very poor reverse of it 

 occur on the same stone with Spiladomijia simplex. Both wings and the 

 thorax are preserved, with short fragments of moderately stout hairy 

 legs. The venation is obscure, and the species referred provisionally to 

 Reteromyza until better specimens decide more certainly to which of the 

 groups oiMuscidce it belongs. The venation is very similar, so far as it 

 can be determined, to Bet. senilis Scudd. from the Tertiaries of British 

 Columbia, but the former species is much smaller, and there is a pecu- 

 liarity about it which is not quite clear : at the bend of the costa, in- 



