June, 1908.] Guatemalan Hemiptera. 379 



The median yellow spot of the niesosternum is sometimes 

 almost lacking and in one specimen the whole body, including 

 antennae and legs, is almost entirely sooty black with scarcely 

 any traces of lighter markings. 



To the upper spine of the first antennal joint in the male 

 are attached a few hairs uniting its apical half with the surface of 

 the joint. These hairs are never free, always glued on to or 

 coalescing with the spine. 



In the larva the mesonotum has a median yellow spot touch- 

 ing the anterior margin, as in the imagines of the other species, 

 but this spot entirely disappears in the imago. 



In two of the three previously described species of this genus 

 the hind legs of the male are incrassated, curved and deformed 

 in a curious way with singular chitinous processes, making them 

 unique in their monstrousness among all known Heteroptera. 

 In the male of Rh. praeposterus the hind legs are normal, it being 

 the middle pair of legs which is misshapen and this only in a mod- 

 erate degree. 



The male antennae afford good specific characters for the dif- 

 ferent species of this genus and their structure is very remarkable 

 and unprecedented among other Heteroptera. They much re- 

 mind of the male antennae in the Collembolan genus Sminthu rides 

 and it would be interesting to know if they are used in the same 

 manner as in Sminthurides, the male of which winds them round 

 the antennae of the female during the copulation. They seem 

 at least admirably adapted to this purpose. Or else could they 

 be of use in clinging to stones, etc., when the insects are drifting 

 down on swiftly running water. This is, however, less probable 

 as the females have simple antennae. An other point of interest 

 is that some of the spines and chitinous processes of the male 

 antennae and legs seem to be composed of hairs cemented to- 

 gether by some viscous fluid. These insects probably have some 

 glands secreting such a fluid. Under the microscope the last 

 antennal joint shows several sense-organs and at the very tip an 

 excavation bearing a short brush. A brush is also situated at 

 the inner end of the fore tibiae. The spongy pit at the apical 

 part of the third antennal joint may also be a sense-organ or pos- 

 sibly a suctorial organ. Unfortunately little is known of the 

 biology of these insects although two species are common at cer- 

 tain points near the Atlantic coast, for instance at Glen Echo, 

 Maryland. As they thrive only on running water it would be 

 difficult if not impossible to rear and study them in aquaria. 

 No species of the genus has hitherto been found far from the sea- 

 shore and none is known from the Pacific Coast. Entomologists 

 in Southern California should keep a lookout for them. 



Riley made a strange mistake in regarding Rh. Rileyi Bergr. 

 and Rh. tenuipes Mein. as the "abnormal" and "normal" form 

 of one and the same species and thus they are generally designated 

 in American collections. There cannot be the faintest doubt 



