On Aquatic Carnivorous Coleoptera or Dytiscidce. 890 



horni this piece is only about 2j times as long as broad. In many other respects 

 however the genus undoubtedly comes near Meladema. The prothora,x is without 

 side margin ; the prosternal process is rather broad, distinctly compressed ; the 

 metasternal groove is imperfectly developed ; the wings of the metasternum are 

 not large, (in Scutopterus horni they are decidedly small) ; the coxal lobes have a 

 considerable extension in the transverse, but little in the longitudinal direction. 

 The swimming legs are rather slender especially the tarsi, and the lamina of the 

 femora is rounded at its outer angle; the terminal joint of their tarsi is elongate, 

 longer than the preceding one, and their lower claw is very long, t\Yice as long as 

 the other. 



The species of this interesting and isolated genus are peculiar to the northern 

 parts of North America, and are still rare in collections. 



I. 62.— Genus RHANTUS. {Vide p. 607.) 



This is an extensive aggregate, with forty species : the size of the individuals is 

 moderate (from 8 to 15 m.m. of length). The side pieces of the fourth and following- 

 ventral segments are very narrow ; the metasternal groove is distinct and Avell- 

 defined, and the terminal joint of the hind tarsus is not longer, (or is but little longer) 

 than the preceding one. 



The numerous species are distinguished constantly from their allies by the above 

 characters, as well as by two others, which are not quite so constant, these are first 

 that the prothorax has a distinct lateral margin, Nos. 957, 958, and 959 being 

 however exceptions in this respect ; and second, that the swimming legs are rather 

 well developed, the femora having their undersurface forming a developed lamina 

 towards the extremity. The colouration of the upper surface usually is yellow, 

 with black specks on the wing cases, but in some species it is entirely black, and in 

 other cases nearly so ; where the wing cases are nearly but not quite entirely black 

 it is generally the margins that are pale, and the black colour seems to have been 

 produced by a coalescence of the black specks. The prosternal process is moderate 

 in length, never elongate, nor very short, and neither slender nor broad, always 

 distinctly compressed. The metasternal groove though not elongate is perfectly 

 well developed, the middle coxse never being so much approximated as to interfere 

 with its development, and it has therefore always perfectly distinct sides ; the coxal 

 lobes are broad and the division between them extends far forwards (except in 

 Colymbetes capensis (No. 957) and Rhantus goudoti (No. 958), which depart from 

 the other species in this respect ; the supra articular border is narrow ; the coxal 

 lines are much separated in front ; the side wings of the metasternum are variable in 

 size, but are never very small. The swimming legs are well developed in some species 

 such as Rhantus goudoti (No. 958), and Dytiscus calidus (No. 942), but are more 

 slender in others, especially in Colymbetes pacificus and other species placed near the 



TRANS. ROY. DUB. SOC, K.S., VOL. II. 5 Z 



