220 GEO. H. HORN, M. D. 



Synopsis of the species orCYniTODERi and TRICIIODEA 

 of the United Slates. 



BY GEORGE II. HORN, M. D. 



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The following paper is presented to the students of our fiuna, with 

 the hope that the recognition of our species raay be rendered more 

 certain and easy of accomplishment, the descriptions being so widely 

 scattered. 



The most recent synopsis was published by Dr. Leconte, (Ann. Lye. 

 v., p. 15), and contained but seven species. In the meantime, a still 

 greater number have been described, and in the present essay three 

 more will appear. 



This great increase in the number of species, has rendered it abso- 

 lutely necessary to seek for characters to separate them, other than 

 those of color or sculpture, as there are certain forms so nearly alike 

 superficially, as to render it almost impossible to separate them even 

 by comparison, while the descriptions give no certain clue. 



The antennae have given me the means of dividing the genus 

 into six primary groups, five being represented by one species each. 

 Secondarily, the structure of the terminal abdominal segments, ven- 

 tral and dorsal, are extremely useful. Finally, two species are apte- 

 rous, although they belong, sexually, with the six species which 

 immediately precede them. 



In species six, seven, and eight, in the accompanying table, the last 

 ▼entral segment is smaller than the last dorsal, so that when viewed 

 from beneath, the edge of the dorsal is visible beyond that of the 

 ventral. In the species which follow, the ventral is large and almost 

 completely hides the dorsal, and its lateral margins are refloxed and 

 partially enclose the pygidium. 



In the accompanying table, the division is not in all cases carried to 

 the point of separating the species individually. In these instances, 

 the separation must be based on sexual characteristics, as no descrii»- 

 tion, however detailed, will serve to distinguish the species if the 

 sexual characters are omitted. 



With this brief prelude, the reader is referred to the following 

 table : 



