JakovL, rated by Zimmermann as a subgenus of Gaurodytes, and for 

 the present I content myself with placing them at the head of our 

 series of species, where they constitute a very distinct group of prob- 

 ably subgeneric value. 



Sharp regarded the genus Agabus as one "of extreme difficulty, so 

 far as regards the determination of species." He arranged the species 

 in twenty-three groups, "some of them natural, some clearly artificial," 

 but made no attempt to tabulate either the groups or the species within 

 them. Zimmermann 1 in his recent work declares himself completely 

 baffled in his attempts to define natural groups in Agabus on external 

 characters, but he has established three sections of the genus based 

 on differences in the genital armature in the males. I am by no means 

 certain that these constitute natural groups, in fact unless there has 

 been some mistake in the identification of our species, the referring 

 of such manifestly closely allied forms as obsoletus and morosus to 

 different sections would seem to militate against it. I shall therefore 

 for the present not attempt the subdivision of the genus into groups, 

 but will present our species in a single table, the mutual relationships 

 being indicated so far as may be by the tabular arrangement and by 

 comments in the text. 



After eliminating cordatus, rectus and clavatus, I shall follow Sharp 

 in using as a first criterion the form of the prosternal process. There 

 is really no well marked line of demarcation anywhere between the 

 broader and flatter form generally characteristic of this process in the 

 species at the beginning of the table, and the narrower strongly convex 

 or carinate form prevailing further along in the series, so that care 

 must be taken to check up conclusions by means of correlative 

 'characters, while a few correctly determined species as standards of 

 reference will be of material service to the student. The sexual 

 modifications of the male pro- and mesotarsi, more especially of the 

 protarsal claws are of much importance in the determination of species 

 and should always be accurately noted. About the only other character 

 used, of which preliminary mention need be made, is the sculpture 

 of the elytral surface. This consists universally of a reticulation, of 

 which the meshes vary greatly in size, form and degree of uniformity 

 in the different species, a minutely critical examination of which is 

 necessary for the successful use of the table, and which will always 

 prove of the highest value in the identification of the rather numerous 

 species which to the casual glance, or under too low amplification, 

 seem monotonously similar. It may aid in the interpretation of the 

 descriptions to say that the strongest obtainable simple lens a one- 

 fourth inch triplet has been usd in my own study. 



iDie Schwimmkafer des Deutschen Entomologischen Museums zu Berlin Dahlem. 



