194 RHYNCHOPHORA. 
Their distribution extends to all timber-producing countries, but, unlike Tomicus, 
they occupy a very subordinate place in temperate regions, to become abundant and a 
dominant genus in the tropics. Here many of the smaller forms have an enormous 
range, and thereby give rise to various difficult problems, economic and systematic. 
Exclusively ambrosia-feeders, they thrive exceedingly in spite of the constant inter- 
breeding that the degeneration of the males necessitates, and are associated with many 
forms of injury. Cacao-trees in Java, tea-plants in Ceylon, fruit-trees in Europe and 
North America, beer-barrels in India, aud hot-house orchids, are among the manifold 
victims of their destructive capacity. | 
The species differ remarkably in shape among themselves, perhaps more so than in 
any other genus of Coleoptera, but preserve a characteristic common habitus which 
rarely leaves room for any doubt in referring an example to the genus. 
It has been recently stated that the classification of the genus presents great diffi- 
culties and is at present in much confusion. This is scarcely correct, except 1n so far 
that the increase in the number of described forms has rendered Eichhoff’s admirably 
clear descriptions and tables non-representative of existing knowledge. In no genus 
of Scolytidz, considering its size, is identification so easy, the only exception being in a 
group of small and widely-distributed forms (vide infra: X. torquatus and X. affinis), 
strongly represented among the United States species, which the writer in question had 
in his mind. But even among these there is little trouble in referring most examples 
to their species, or to one of two species, by the aid of Eichhoff’s descriptions alone, 
the real difficulties arising from the fact that the “species” are found to be connected 
by intermediate forms which cannot be placed except arbitrarily. ‘Troublesome as 
such problems are, they are met with in every branch of zoology and botany and are 
beyond the power of ordinary methods of classification to solve. 
In comparison with Pycnarthrum, Cryphalus, Hypothenemus, or the Platypi trispinati, 
even the Xylebori of the torquatus-group are easy to study. 
A small number of Oriental species have been separated from AXyleborus to form the 
genera Eccoptopterus, Motsch., and Progenius, Blandf.; but the genus does not seem to 
admit of further division, which, indeed, is not required. Ferrari’s genus Anisandrus, 
based on the male characters of a few species, is absolutely worthless, and it is surprising 
that it should still be employed at all. 
As with Platypus, it is necessary to tabulate the sexes separately. Owing to the 
small number we possess, the dichotomous table of the males is useful only as an 
indication of the probable affinities of any form that may be placed by it. 
Males. Prothorax usually depressed or broadly impressed anteriorly, with feeble asperities, its 
anterior margin sometimes excised or armed; body relatively smaller and less robust, 
subapterous. 
Females. Prothorax not depressed or impressed in front, more strongly asperate, the anterior 
