On Aquatic Carnivorous Coleoptera or DijtisckUe. 919 



which is not found in any of the other groups, viz., that the swimming feet in this 

 sex are furnished beneath with swimming hairs along their outer edge, hke the 

 males, whereas in all the other groups only the males have the swimming tarsi 

 ciliate in this manner. 



Species of this aggregate are found in most parts of the eastern hemisphere, and 

 in North America, but are wanting in South America, one of the species, Dytiscus tn- 

 punctatiis has a very wide distribution from Japan, Australia, and New Caledonia, 

 through the Philippine and Malay Islands and Asia, to Africa, and Southern 

 Europe ; and appears to be the most abundant species of the family Dytiscidas. 



SECOND SYNTHESIS. (GROUPS) 



II. 1.— Group NoTERiNi. (Fide p. 26.3.) 



Three genera, one of which is an autogenus, while the other two contain each six 

 species, form this secondary aggregate. The size of the individuals varies from 2i 

 to 5 m.m. of length ; the form is very constant, transversely very convex above, 

 almost flat beneath, the outline very continuous, forming an oval attenuate behind, 

 there is no variegation of the upper surface, and the sculpture is peculiar, consisting 

 of more or less isolated large punctures on the wing-cases (sometimes peculiarly 

 asperate), and more or less completely wanting on the basal portion. The antenna are 

 very variable, but sometimes show a most remarkable and extraordinary form in the 

 males. The anterior tibife bear a more or less elongate curved spur, and their 

 outer angle is either conspicuously prominent (Pronoterus) or quite rounded off 

 (Synchortus, Noterus.) The prosternal process is never large, sometimes very short 

 and small, it is either rounded or obtusely acuminate behind. The suture between 

 the hind coxa and metasternum approaches very near to the middle coxa ; the 

 hind coxal cavities are contiguous, and the swimming legs are either moderately or 

 well developed ; the hind margin of their femur is destitute of any group of ciliae 

 at its extremity, and the lower face of the femur is either impunctate (Pronoterus) 

 or furnished with a transverse series of conspicuous punctures, extending somewhat 

 parallel with, but at a distance from, the hind margin. 



The geographical distribution of the species of Noterini, is in accordance with 

 their arrangement in genera, viz : tropical South America, one species (an autogenus) ; 

 European region and Japan, six species (forming one genus) ; Madagascar and tropical 

 Africa, six species (forming one genus). 



The South Aoierican insect is the lowest of the forms, and it is doubtful whether 

 on the whole the European Noterus or the Africo-madagascarene Syrchortus is the 

 higher form. It seems probable that the centre of distribution is either Madagascar 

 or tropical Africa. 



