1896 Insects. 



Genus Hydaticus, Leach. 



1. H. transversalis, Fabr., Panz., Steph., &c. 



2. H. Hybneri, Fabr., Oliv., Steph., &c. 



3. H. stagnalis, Fabr., Gyll., Steph., &e. 



4. H. cinereus, Payk., Gyll., Curt., Steph., &c. 



In Linne 's collection three different insects are confounded under the name of 

 Dy. cinereus, viz., H. zonatus, Hoppe, H. bilineatus, Degeer, and the female of 

 Acilius sulcatus. 



Genus Dytiscus, Linne. 



1. D. circumcinctus, Ahrens, Gyll., Steph., Sturm, Aube, Erichs. 



$ var. elytris sulcatis : D. dubius, Gyll., Aube. 

 D. angustatus, Steph. 



2. D. marginalis, Linne, &c. 



— submarginalis, Steph. 111. 



$ var. elytris laevibus: D. conformis, Kunze, Steph., Aube. 



3. D. circurnflexus, Fabr., &c. 



$ var. elytris sulcatis : D. perplexus, Aube. 

 The three preceding species have two forms of females, one with smooth, the other 

 with sulcated elytra. Of D. circumcinctus the smooth females are the commoner, the 

 sulcated the rarer ones; of D. marginalis both forms are nearly equally common ; of 

 D. circurnflexus the continental females are smooth, the sulcated, described by Dr. Aube 

 under the name of D. perplexus, being exceedingly scarce ; the British females of this 

 species which I have seen are, on the contrary, all sulcated. Some authors think that 

 the smooth and sulcated females belong to different species ; and the Rev. W. Kirby 

 has even divided them into the genera Leionotus and Dytiscus, the former including 

 the species with smooth, the latter those with sulcated elytra ; but as the males are per- 

 fectly alike, and as the same discrepancy among the females has now been observed in 

 four European species (the three above named and D. lapponicus), and as two forms of 

 females occur also in some species of Hydroporus (H. picipes, erythrocephalus and 

 unistriatus, one with shining, the other with an opaque and more finely punctured sur- 

 face), I think the opinion of Erichson, which I have followed, may be considered as 

 sufficiently established. 



4. D. punctulatus, Fabr., &c. 



5. D. dimidiatus, Bergsti> &c. 



Genus Cybister, Curtis. 

 1 . C. Rceselii, Fabr., &c. 



Genus Acinus, Leach. 



1. A. sulcatus, Linn, &c. 



— scoticus, Steph. 111., var. 



2. A.fasciatus, Degeer, Erichs., Steph. Man. 



— canaliculars, Nicolai, Steph., Aube. 



— caliginosus, Curtis. 



— sulcipennis, Sahib. 



