198 GEO. H. HORN, M. U. 



Synopsis of the THRO»«CID.K of the United States. 



BY GEORGE H. HORN, M. D. 



The small series of insects contained in this family seems to have es- 

 caped attention in our fauna with the exception of the description of a 

 few new species by Dr. LeConte. 



Three genera are known in our fauna which may be separated in the 

 following manner : 



Antennae with the hist three joints abruptly larger; metasternqin obliquely 

 grooved for the reception of the middle tarsi Throscus. 



Antennae fusiform; raetasternum and first three segments of abdomen obliquely 

 grooved for the reception of the middle and posterior tarsi Psictopus. 



Antennae serrate from the third joint; tarsi free, not received in grooves. 



Drapetes. 



Throscus is represented on both sides of the continent, Pactopus in 

 the Pacific and Drapetes in the Atlantic region. 



THROSCUS Latr. 



The generic characters have so often been given that it is hardly nec- 

 essary to dwell further on them. There are, however, some diflferences 

 of structure within generic limits to which it may be useful to call 

 especial attention as they supply characters of great use in grouping and 

 dividing the species. 



In his admirable essay (Essai mouographique sur la famille des Thros- 

 cides, Paris, 1859) Bonvouloir indicates important modifications of the 

 eyes, which may be grouped in three series. In the first the eyes are 

 oval in form and entire, the second is that in which the front of the eye 

 is broadly triangularly emarginate, while in the third an oblique narrow 

 depression very nearly divides the eye into two nearly equal portions. 

 These three forms give a very natural primary grouping of the species. 



The second character of moment is the mode of striation of the pros- 

 ternum. In nearly all the species the striae are entire, extending from 

 the point of the prosternum forward to the anterior margin, and in most 

 cases exactly parallel, but in a few divergent. There are, however, spe- 

 cies in which the striae are abbreviated, in which case the middle of the 

 prosternum in front is more distinctly punctate. 



