92 GEO. H. HORN, M. D. 



same view is maintained in the Classification of the Coleoptera of North 

 America. Chaudoir (Bull. Mosc. 1872), says : " notwithstanding the 

 opposition of many entomologists, this genus can be placed only in the 

 vicinity of Trachypachya, as a distinct group." 



Dr. Sharp in the paper above cited claims for Amphizoa a place in 

 the Dytiscidae in the series Dytisci comph'cati^ which have the meta- 

 sternal episternum taking part in the closure of the middle coxae. This 

 character which I first observed in Amphizoa and illustrated by a figure, 

 (Trans. Am. Ent. Soc. 1867, p. 157), appears to have caused Dr. Sharp 

 to arrive at the above conclusion. I believe Amphizon to be far less 

 a Dytiscide than a Carabide. 



The series in which Dr. Sharp places Pelohius is called Dytixci frag- 

 mentati which is characterized by the less complex structure of the outer 

 side of the middle coxal cavities. Here the same number of pieces are 

 found which we observe in the sub-family Carabinag, that is, the meso- 

 sternum, its epimeron and the metasternum. These two series of Dytiscidae 

 Dr. Sharp very aptly compares with a similar division of the Carabidae 

 in two series, in which the D. fragmentati represent the more highly 

 specialized Carabinae and the D. compUcatl the Harpalinae. In Amphizoa 

 and Peiobius I see two distinct types each with a very evident Carabide 

 relationship and intermediate between the Carabinas and Dytiscidae in 

 two distinct lines. The Carabinas seem to be a centre from which the 

 other Carabidae and the Dytiscidae diverge, the former toward a simpler 

 the latter to a greater degree of complication of the coxal structure. 



Peiobius was accepted by Lacordaire and many since as an undoubted 

 Dytiscide with certain aberrant characters. Dr. Sharp, while admitting 

 that it has but little claim to such a position, places it at the head of 

 that family notwithstanding that he says, "the Carabide predominates 

 over the Dytiscide in its organization." That he acts thus with impartial 

 fairness to two very aberrant genera, must be admitted, but I hope to 

 show that in all the Adephaga there exist characters of very great 

 systematic importance which have been entirely overlooked and which 

 will define with great accuracy the relationship of the various families. 



It must be evident to all that there are radical diiferences in the 

 formation of the under side of the body in the now recognized families 

 of the Adephagous series. Many of the characters making up these 

 difi"erences have been made use of by various authors and they have 

 now become the common property of the science. 



The structure of the metasternum demands a new study and here will 

 bo found the important characters to which I have already referred. 



