of the Amazon Valley. 181 
The absence of seven of these may be explained by the fact of their 
being found only in mountainous regions, or at least in warm valleys 
of a greater elevation than any part of the Amazons country. These 
are Gnathotriche, Synchloé, Pyrameis, Cybdelis, Epiphile, Perisama, 
and Pycina; Pyrameis being a genus characteristic of the temperate 
zones of the whole earth, but found only in elevated places in the 
neighbourhood of the equator, and quite absent from the banks of the 
Amazons. Two other genera (Clothilda and Lucinia) are peculiar, or 
nearly peculiar, to the West India Islands, and therefore could not be 
expected to occur in the Amazons region. The same might have been 
anticipated of two others, Morpheis and Cymatogramma, which inhabit 
only the northern part of Tropical America. If we withdraw two of 
the remaining six, namely, Callitenia and Batesia,—which, although 
not observed along the centre of the Amazonian plain, inhabit its 
northern and western confines,—there remain four whose absence can 
with difficulty be accounted for, as they are mostly very common 
insects, apparently in low-lying regions, to the north and south of the 
Amazonian plains, and yet are entirely absent from the intermediate 
country. These are,—1l, Hurema, which has representatives in New 
Granada, Guatemala, and Mexico, to Texas and Kansas, and again 
in South Brazil—one species, indeed (EZ. Lethe), being common to 
these two opposite quarters—but yet is entirely wanting throughout 
the whole equatorial region of the Amazons from east to west; 2, 
Heematera, the species of which, inhabiting South Brazil and Vene- 
zuela, seem to be local varieties of one and the same stock; 3, Am- 
phirene, of which precisely the same may be said; and lastly, 4, 
Smyrna, whose two species, like Hurema Lethe, are very common 
insects from about 23° to 30° S. lat., and from 6° (probably at an 
elevation) to 16° N. lat., and yet are completely unknown in the 
intermediate Amazonian region. The explanation of these anomalies 
in distribution seems to require the former existence of greater 
facilities than now exist for the migration from northern to south- 
ern regions (or vice versa) of insects which are apparently unable now 
to sojourn in the intermediate forest-plains. This very interesting 
question, however, which involves considerations regarding geolo- 
gical and climatal changes that may have supervened in tropical and 
subtropical America since the date of the first appearance of ex- 
isting species, cannot be entered into in detail until we have much 
more exact information of the range of genera and species (common 
to north and south, but absent at least from the plains of the inter- 
mediate equatorial zone) along the line of the Andes, under the 
equator. It may be that such genera and species find even now a 
