240 GEO. H. HORN. 



standing the fact that our species possesses the essential characters 

 of Chasmogenus, even to its manner of niesosternal variation, I am 

 disposed to place it with Helochares, the more so as it resembles very 

 closely the species already placed there. While I am not prepared 

 to say that Chasmogenus should be suppressed (not having seen a 

 typical species), I am rather disinclined to admit the name in our 

 fauna for a species which has all its essential characters. 



The genera which follow in the table, Cymhiodyta and Hydrocombus, 

 are well separated from the others by the 4-jointed middle and hind 

 •tarsi. These two genera are said to differ in the structure of the 

 mesosternum. To Dr. Sharp I am indebted for the species ty|)ical 

 of Cymbiodyta {rnarglnella Fab.), although Bedel mc\w.6ie^ jimbriata 

 in it. An examination of our species and marginella shows plainly 

 what has already been indicated, that all the forms of niesosternal 

 protuberance, except in Philydrus are derivations from a transverse 

 ridge. In our fauna the simplest form is seen in lacustris, from which 

 the ridge first becomes longer, then arched, then elevated in its mid- 

 dle, so that Avhen viewed directly from behind the ridge is in form 

 like A, the entire elevation being somewhat pyramidal in form. 

 These variations are illustrated on PI. iii, fig. 18, a, b, c, d, e. I 

 have, therefore, no hesitation in asserting that Hydrocombus cannot 

 be separated from Cymbiodyta. To Cymbiodyta should be referred 

 all those species formerly placed by me in Helochares, except macu- 

 UcoUis. 



On the other hand one of our species with the tarsal structure of 

 Cynibiodyta cannot be referred to it. The mesosternum in front of 

 the coxa? is elevated in a rather .slender, compressed conical process, 

 and the claw^s are abruptly dilated in the male at base, less in female. 

 The jialpi are also very long and slender. For the species bifidus 

 Lee. I propose the generic name Helocombus. 



The genera which are known to occur in our fauna and seem en- 

 titled to recognition are as follows : 



Tarsi S-jointed on all the feet. 



Pseudo-basal joint of maxillary palpus curved with the convexity anteriorly; 

 mesosternum with a longitudinal lamina ; tarsal claws toothed in male 



with few exceptions Philydrus. 



Pseudo-basal joint curved with the convexity posteriorly; mesosternum, at 



most, feebly protuberant; tarsal claws simple Helocliares. 



Tarsi 4-jointed on the middle and posterior feet ; pseudo-basal joint of maxillary 

 palpus either straight or slightly curved posteriorly. 



