934 On Aquatic Carnivorous Coleoptera or Dytiscidce. 



between tlie broad form displayed by the pieces iu the Agabini and the narrow one 

 usually found in the Colymbetini. Thus in Matus the side piece of the fourth 

 segment is as broad as in the genus Agabus, while in Coptotomus it is hardly broader 

 than it is in certain members of the Colymbetini (Dytiscus grapii, No. 943, for 

 example). In this respect therefore these genera connect the Agabini and Colymbetini. 



In most of the several genera the posterior portion of the metathoracic epister- 

 num where it is exposed between the wing of the metasternura and the epipleura 

 is very attenuate and acuminate; this is especially the case with Copelatus, Aglym- 

 bus, Lacconectus, and Matus; while in Coptotomus the wing of the metasternum 

 has so great an outward extension that it is almost invaded by the epipleura, that 

 is to say that its termination cannot certainly be distinguished without slightly 

 raising the epipleura from the breast. Thus this genus which by its ventral side 

 pieces approximates to Colymbetini, by its metathoracic structure departs mostwidely 

 therefrom. On the other hand Lancetes has the posterior extremity of the epister- 

 num comparatively broad, and the apex of the wing of the metasternum distinctly 

 though slightly separated from the epipleura, thus making an approximation to the 

 Colymbetini. 



In these genera, the setigerous abdominal pores, relied on by Thomson as 

 distinguishing the Agabides from the Colymbetides, undergo much vai'iation ; they 

 are distinct on the fourth and fifth segments, but are wanting on the third in 

 Lancetes and Coptotomus ; they are present on the third, fourth, and fifth segments 

 iu Matus, but are only very slightly impressed ; they are present on the three seg- 

 ments but are very small in Copelatus and Agiymbus; in Lacconectus they are 

 also present but are so minute and rudimentary that they can scarcely be detected; 

 and in Agabetes they are altogether wanting. 



II. 11. — Group Colymbetini. (F^fZe p. 605.) 



This aggregate is formed by four genera (comprising sixty-two species) ; the 

 individuals are of moderate or rather large size, varying from 8 to 21 m.m. in length, 

 and the surface is not punctate, but is either nearly smooth or possesses on the 

 wing-cases a peculiar sculpture, wliich may be either reticulation or transverse 

 scratching (aciculation), or even a kind of faintly raised sculpture having a slightly 

 imbricate appearance. The semimembranous side piece of the first segment of the 

 hind body {i.e., the part interposed between the stigma and the edge of the ventral 

 plate) is marked by transverse rugse or furrows ; when tliere are any setigerous 

 punctures on the hind femur, they form an irregular patch at the extremity, not 

 however close to the hind margin, but widely separated therefrom. 



The most important of these characters is the presence of the stigmatic rugte, and 

 it is the possession of these rugte that decides absolutely that a species shall be placed 

 in the Colymbetini rather than iu the Agabini. These rugte are found outside the 

 limitsof the Colymbetini only in the two genera Hyderodes and Dytiscus (formingthe 



