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 

 lo7igiusculus group and most unstable in the binotatus 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 Echiastei\ 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 eraargination 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, transver^ie, 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 moderately 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- 



