AMERICAN COLEOPTERA. 137 



Revision of the species of LISTROCHEIiUS of the United 



States. 



BY GEORGE H. HORN, M. D. 



The present essay is intended as the commencement of a work 

 which has long seemed necessary, a new revision of our Melolonthidae. 

 Since the first revision, (Leconte, Journ. Acad. Ser. 2, vol. ii, 1856), 

 some few new species have been described, a few then unknown re- 

 cognized, some synonymy corrected, while many new species have 

 been discovered and above all much larger series of all accumulated. 

 These facts together with the additional knowledge acquired in the 

 meantime render the labor somewhat easier, on the one hand, while 

 the increase in the number of the species renders the whole mass 

 rather less amenable to classification by the almost inevitable occur- 

 rence of exceptional forms. 



At this point I may mention that the types in the cabinet of Dr. 

 Leconte have been freely at my command, and that Mr. Ulke of 

 Washington, has also loaned his material which has been extremely 

 useful, he having in several species the sex not existing in either 

 Leconte's or my own cabinet. 



In beginning a study of any tribe of Coleoptera the most important 

 work is the generic separation of the mass of species and a determi- 

 nation of the value of the genera themselves. 



The genuine Melolonthini have been divided into three groups by 

 the following table : 



Side pieces of nietathorax narrow; 



Labial palpi on the under surface of the ligula RHIZOTROGI. 



Labial palpi at the sides of the ligula TOSTEGOPTER.ffi. 



Side pieces of nietathorax wide MELOLONTH.ffi. 



In regard to the difference of position of the palpi in the first two 

 tribes above named, I can only say, that after a dissection of the 

 mouth of Tosteyoptera and Lachnosterna I can find no appreciable 

 difference. The group therefore fails and with it the genus which 

 must take its place with the Lachnosternae in the position originally 

 assigned to it by Dr. Leconte. 



TEANS. AMER. ENT. SOC. VII. (18) NOVEMBER, 1878. 



