Casey — A Revision of the American Paederini. 245 
a darker general coloration and differs in several other 
characters. Coloration seems to be most constant in the 
longiusculus group and most unstable in the bénotatus group. 
The beetles of this genus run with very great rapidity when 
disturbed, being relatively more agile in proportion to their 
size than any other Paederids known to me. 
ECHIASTERES. 
The genus Hchiaster, and some others more or less closely 
allied, form a group peculiar to the American continents and 
greatly developed in the tropical regions of South America. 
The Echiasteres are related to the Sunii by the closed anterior 
coxal cavities, the corneous floor of which abuts closely against 
the flanks of the pronotum, in certain features of general 
habitus and sculpture, in the general structure and vestiture 
of the maxillary palpi and in the united gular sutures, but 
differ greatly in the very slender filiform tarsi with the fourth 
joint not lobed, in the extremely short and posteriorly flexile 
antennae, the apex of the very short basal joint being emar- 
ginate posteriorly, in certain structural peculiarities of the 
mentum and in several other directions. The sculpture is 
not very coarse but extremely dense, so that the lustre is 
densely dull, and the vestiture .is in the form of very short, 
thick, closely recurved pale hairs, entirely inconspicuous except 
under considerable magnifying power. The two genera known 
thus far to enter our territories may be defined as follows: — 
Fifth and sixth ventral segments prolonged, narrow and subtubulate; eyes 
very large and.conspicuous, completely nude; body rather small and 
moderately slender, the head well developed, orbicular, the labrum short, 
broadly rounded at tip, with a small angulate median emargination and 
four equal small and broadly angulate teeth; antennae but little longer 
than the head, the funicle slender at base, rapidly incrassate distally; 
mentum small, transverse, the sides elevated, forming ridges which are 
prolonged before the apex as slender aciculate processes, each bearing 
a short axial apical seta; labial palpi small, slender, the maxillary well 
developed with the second joint raoderately stout, arcuate, short and 
nude, the third oval, feebly compressed, finely and densely pubescent, 
more arcuate anteriorly than posteriorly and longer than the second, 
the fourth small, short, obliquely conical and pubescent, very incon- 
spicuous; neck very slender, about a sixth as wide as the head; protho- 
