412 CHAEACTEES OP THE GENUS TACHYCINETA 



taxed to supply voracious throats with insects captured on 

 tireless wing. The rate of speed in flying, the distances tra- 

 versed in a given period, and the numbers of insects destroyed, 

 have all been the subjects of some curious calculations, — or 

 rather speculations, for these matters scarcely admit of mathe- 

 matics. Wilson supposed a Swallow to fly about a mile a 

 minute, for ten hours a day, for ten years, — equivalent to more 

 than eighty-seven times around the world ! However this may 

 be, let us trust that these matchless wings may bring the iSwal- 

 lows again next year, as they have this; and let us look leni- 

 ently, even encouragingly, upon the various superstitions of 

 folk-lore, which tend to protect and foster these amiable, these 

 charming and useful creatures — even though we may not fear 

 that to kill them is to make the cows give bloody milk ! 



Genus TACHYCINETA Cab. 



HIrnndo, p., of natbors. 



GhelidoD, Boie, Isis, 1826, nee 1833 (originally applied to H. urbica). 



Tacbf clnetn, Oa,i. Has. Hein. L 1850, 48 (type H. Uialassina,). 



This group was established in 1850 by Cabanis upon H. 

 thalassina of Swainson, and is now commonly allowed to 

 include H. bicolor. These species agree closely with each other, 

 both in form and pattern of coloration, and differ from Hirundo 

 proper chiefly in lacking the disproportionate length, attenua- 

 tion and forfication of the tail, this member being much shorter 

 than the wiugs, and simply emarginate or with shallow fork. 

 All the species are entirely white below, and the extralimital 

 ones, of which there are several, have the rump white. The 

 eggs of our species are pure white, unmarked. H. thalassina 

 stands alone in the soft velvety plumage of the upper parts, 

 without metallic gloss, and much variegated in color. The 

 other species, including T. bicolor, have more compact, silky 

 plumage, with rich metallic sheen. A difference was noticed 

 by Cabanis, who speaks of T. bicolor „ als 2te, jedoch vom 

 Typus mehrfach abweichende Art." None of the many 

 generic names bestowed of late upon Swallows have been 

 based upon T. bicolor, which seems at least as worthy as some 

 others to stand as type of a subgenus (Iridoprocne). This 

 includes, besides /. bicolor, the extralimital species I. albiven- 

 tris, I meyeni, I, leucorrhoa, I. albilinea, and probably some 

 others. The whole group is confined to America. Both of the 

 North American species occur in the Colorado Basin. 



