

XIII. Prodrome of a Monograph of the Tab.vxid.e of the United States. Part I. 

 The Genera Paiigonia, Chrysops, Silvius, Haematopota, Diabasis. By C. R. Osten 



SacKEjST. 



Read January 6, 1875. 



J. HE purpose of the present paper is to pave the way for a future monograph of the 

 Tahanldcii of the United States. In a fixmily as difficult as the present, a preparatory pa- 

 per of this kind does good service in encouraging collectors and disclosing the doubtful 

 points which can be solved only by an increase of material. 



A conscientious monograph requires, besides specific descriptions, a thorough investiga- 

 tion of the generic and family characters, based upon the knowledge of the generic forms 

 of the whole world. My present purpose being merely the discrimination of the species, I 

 refer, for the definition of the genera, to the existing works on the subject. I would espec- 

 ially recommend the chapter on Tahanidos in Dr. Loew's large work : Die Dlptern-Fauna 

 Sad-Africa's, in which a critical review of the whole family and of all the adopted genera 

 is given. A similar review will be found in Dr. Schiner's Diptera of the Novara expedition. 



The types of all the descriptions given below are to be found in the Museum of Compar- 

 ative Zoology, in Cambridge, Mass., unless otherwise mentioned. 



The following tabular arrangement has no other claims than to embrace the genera and 

 species contained in the present paper. 



TABULAR ARRANGEMENT OF THE NORTH AMERICAN GENERA OF TABANID.S;. 



r Hind tibijB with spurs at the tip. Ocelli in most cases present 2. 



* 1 Hind tibiiB without spurs ; no ocelli 4. 



J Face and front (?) without tubercles or callosities Pangonia. 



'1 Front (?) provided with a tubercle or callosity 3. 



fSecond antennal joint .almost as long, or as long, as the first; wings with a black or brown 

 3. ^ design Chrysops. 



[Second antennal joint very much shorter than the first; wings without any spots .... Silvius. 



Front ( 2 ) much longer than broad ; frontal tubercle (when present) not transverse . . | Diabasis" 



4- i Front (?) as broad as it is long, or broader; frontal tubercle transverse (about four times broader than 



I long) • • Haematopota. 



PANGONIA. 



The described species from the United States (with the exception of F.fusiformis Walk.) 



may be tabulated as follows : — 



. r Proboscis longer than the whole body macroglossa Westw. 



I Proboscis not much longer than the head 2, 



JIEU0IR3 B03T. SOO. XAT. HIST. VOL. U. *2 (365) 



