744 THE AMERICAN NATURALIST [Vol. L 



villiform, and usually occur only in the jaws. The pharyn- 

 geal bones, unlike those of the true minnows or cy- 

 prinoids, often have fine teeth, rarely molar, and never 

 modified or in even numbers as in cyprinoids. The scales 

 are mostly large, cycloid, adherent, regular and without a 

 perfected lateral line. The dorsal and anal fins are single, 

 inserted usually behind the middle of the body, but no adi- 

 pose fin developed. The caudal is broad and, though 

 sometimes pointed, not forked. The paired fins are placed 

 low, and the ventrals abdominal. 



Many genera and species, about sixty belonging to the 

 first and over three hundred to the last, have been de- 

 scribed. Of these about ten genera and fifty species occur 

 in the United States. The family reaches its greatest di- 

 versity in tropical America, and in the Old World the 

 largest number of forms occur in African fresh waters. 

 Killifishes live in fresh waters in nearly all situations, in 

 lakes of great elevation, or in sandy desert streams, pud- 

 dles and ponds. Others live in tidal waters, or along the 

 shores of sea-beaches, and all near or close to the surface. 

 The great changes with age, sex and season render many 

 of the species difficult of determination. All are of small 

 size, less than a foot in length. 



In nearly all killifishes the sexual differences are well 

 marked, at least during the spawning or breeding season. 

 Often the males have enlarged fins, smaller in the females, 

 as in the may-fish (Fundulus majalis) and the zebra- 

 fish (Fundulus zebrinus). Still other characters occur in 

 some species which have been entirely overlooked or 

 scarcely noticed by most writers. These are the minute 

 spines, or spinules, adorning the scales and fin-rays of 

 certain species during the spawning-season. Garman, in 

 his celebrated monograph of the killifishes, 1 simply says, 

 "a minor sexual character is that of small spines appear- 

 ing on the fins of males in several genera in the breeding 

 time." I have been unable to find any detailed account 

 of these structures, except casual reference to a few in 

 descriptions of species. These are usually quite short and 



i Mem. Mug. Comp. Zool., XIX, 1895, p. 11. 



