Xystosomus impressifrons, Erwin, 1973, Erwin, 1973

Erwin, Terry L., 1973, Studies of the subtribe Tachyina (Coleoptera: Carabidae: Bembidiini), Part I: A revision of the Neotropical genus Xystosomus Schaum, Smithsonian Contributions to Zoology 140, pp. 1-39 : 29

The laexris group

Members of the leavis group are characterized by their broadly transverse pronota, greatly inflated and globular elytra, and small heads, together with

a complete lack of impressed elytral striae, absence or partial absence of lateral pronotal setigerous pores (exception is X. impressifrons , with both sets present), and absence of flight wings. Besides these external characteristics, the internal sac and the apex of the median lobe of the male genitalia share great similarities (see illustrations).

The concordance of the above-mentioned characteristics indicates that the laevis group is a natural group of rather closely related forms that probably underwent speciation after the loss of powers of flight. This view is further supported by the group's very small range. The group is known to be composed of seven species, all of which are found in Brazil south of the Amazon Basin ( Figure 72 ).

Figures

FIGURE 72.—Approximate range of the inflatus and laevis groups.