There are an immense number of species belonging to this genus scattered through the tropical and subtropical regions of both hemispheres. Many of the species are dimorphic or polymorphic, and much confusion has arisen, especially in relation to the Oriental species, on account of the great tendency to the production of seasonal varieties, many of which are strikingly different from one another. (1) =Terias gundlachia=, Poey, Plate XXXVII, Fig. 1, ♂ (Gundlach's Sulphur). _Butterfly._--This species is easily recognized by the orange-yellow tint of the upper side of the wings and the sharply pointed hind wings. Expanse, 1.80 inch. _Early Stages._--We know nothing of these. The species is found in Texas, Arizona, Mexico, and Cuba. (2) =Terias proterpia=, Fabricius, Plate XXXVII, Fig. 2, ♂ (_Proterpia_). _Butterfly._--Even deeper orange than the preceding species. The hind wings are, however, less pointed; the veins and nervules are black at their ends, and the costal margin of the fore wings is evenly bordered with black, which does not run down on the outer margin as in _T. gundlachia_. Expanse, 1.50-1.75 inch. _Early Stages._--Unknown. _Proterpia_ is found in Texas, Arizona, and Mexico. (3) =Terias nicippe=, Cramer, Plate XXXVII, Fig. 3, ♂; Fig. 4, ♀; Fig. 5, var. =flava=, ♂; Fig. 6, ♀, _under side_; Plate II, Fig. 6, _larva_; Plate V, Figs. 51, 52, _chrysalis_ (Nicippe). _Butterfly._--The plate gives so full a presentation of this common species as to make a lengthy description unnecessary. It is subject to considerable variation. I have specimens of many varying shades of orange and yellow, and a few albino females. The orange form depicted in Plate XXXVII, Figs. 3 and 4, is typical. The form _flava_ is not uncommon. Expanse, 1.50-2.00 inches. _Early Stages._--These are not as well known as they should be in view of the excessive abundance of the insect in long-settled parts of the country. The caterpillar feeds upon _Cassia_ in preference to all other plants, but will eat other leguminosæ. _Nicippe_ is very rare in New England, but is common south of latitude 40° as far as the Rocky Mountains, and ranges over Cuba, Mexico, and Guatemala, into Venezuela and even Brazil. It fairly swarms at times in the Carolinas, Tennessee, Kentucky, and southern Indiana and Illinois. I have encountered clouds of it on the wing near Jeffersonville, Indiana, and thence north along the lines of the Pennsylvania Railroad as far as Seymour. It is not common in western Pennsylvania, but in former years was taken rather frequently about Pittsburgh. (4) =Terias mexicana=, Plate XXXVII, Fig. 7, ♂; Fig. 8, ♀, _under side_ (The Mexican Yellow).