Of the many genera of _Pœciliidæ_, top-minnows, and killifishes we may mention the following: _Cyprinodon_ is made up of chubby little fishes of eastern America with tricuspid, incisor teeth, oviparous and omnivorous. Very similar to these but smaller are the species of _Lebias_ in southern Europe. _Jordanella floridæ_ of the Florida everglades is similar, but with the dorsal fin long and its first ray enlarged and spine-like. It strongly resembles a young sunfish. Most of the larger forms belong to _Fundulus_, a genus widely distributed from Maine to Guatemala and north to Kansas and southern California. _Fundulus majalis_, the Mayfish of the Atlantic Coast, is the largest of the genus. _Fundulus heteroclitus_, the killifish, the most abundant. _Fundulus diaphanus_ inhabits sea and lake indiscriminately. _Fundulus stellifer_ of the Alabama is beautifully colored, as is _Fundulus zebrinus_ of the Rio Grande. The genus _Zygonectes_ includes dwarf species similar to _Fundulus_, and _Adinia_ includes those with short, deep body. _Goodea atripinnis_ with tricuspid teeth lives in warm springs in Mexico, and several species of _Goodea_, _Gambusia_, _Pœcilia_, and other genera inhabit hot springs of Mexico, Central America, and Africa. The genus _Gambusia_, the top-minnows, includes numerous species with dwarf males having the anal modified. _Gambusia affinis_ abounds in all kinds of sluggish water in the southern lowlands, gutters and even sewers included. It brings forth its brood in early spring. Viviparous and herbivorous with modified anal fin are the species of _Pœcilia_, abundant throughout Mexico and southward to Brazil; _Mollienesia_ very similar, with a banner-like dorsal fin, showily marked, occurs from Louisiana southward, and _Xiphophorus_, with a sword-shaped lobe on the caudal, abounds in Mexico; _Characodon_ and _Goodea_ (see Fig. 53, Vol. I) in Mexico have notched teeth, and finally, _Heterandria_ contains some of the least of fishes, the handsomely colored males barely half an inch long. [Illustration: FIG. 160.—_Goodea luitpoldi_ (Steindachner). A viviparous fish from Lake Patzcuaro, Mexico. Family _Pœciliidæ_. (After Meek.) ] In Lake Titicaca in the high Andes is a peculiar genus (_Orestias_) without ventral fins. Still more peculiar is _Empetrichthys merriami_ of the desert springs of the hot and rainless Death Valley in California, similar to _Orestias_, but with enormously enlarged pharyngeals and pharyngeal teeth, an adaptation to some unknown purpose. Fossil Cyprinodonts are not rare from the Miocene in southern Europe. The numerous species are allied to _Lebias_ and _Cyprinodon_, and are referred to _Prolebias_ and _Pachylebias_. None are American, although two American extinct genera, _Gephyrura_ and _Proballostomus_, are probably allied to this group.