871 



Mydaidae and Scenopinldae but separated them widely in his later, 

 more comprehensive works, associating the scenopinids with the fami- 

 ly Therevidae, and basing his argument for so doing upon the struc- 

 ture of the larva. In the present paper I have considered the family 

 as belonging to the superfamily Asiloidea. 



FAMII^Y CHARACTERS 



Larva (PI. LIII, Fig. 4). — White, usually very large and robust, 

 with clearly differentiated segments ; head rather large, under a low 

 power appearing like a solid black cone; maxillae chitinized, pointed 

 apically, not abruptly differentiated posteriorly, their inner surfaces 

 clothed with stout, branched spines (Fig. 2) ; mandibles long, curved, 

 slender, their apices extending to those of maxillae and beyond apex 

 of the slender labrum ; surface of head with several long hairs. 

 Thoracic segments slightly tapering anteriorly, only a slight rounded 

 shoulder to anterior margin of first segment ; prothoracic spiracles 

 rather small; metathorax with a pair of small spiracles; the usual 6 

 thoracic hairs, as in Asilidae, present. Abdominal and posterior 

 thoracic segments slightly flattened dorso-ventrally and with a dis- 

 tinct lateral bead-like extension, the segments not as long as their dor- 

 sal width, those of abdomen with a rather abrupt transverse depres- 

 sion along their anterior dorsal margin except in the case of the apical 

 2 ; abdomen with small lateral spiracles on segments 1-7 ; middle ven- 

 tral segments of abdomen each with a transverse series of 4 rather ir- 

 regular pseudopod-like elevations near anterior margin ; penultimate 

 segment with 2 large round spiracles close to anterior margin, and a 

 sharply defined transverse depression on its posterior margin ; apical 

 segment with a rather sharp ridge along the posterior margin, and 

 armed with several hairs. 



Pupa (PI. LIII. Fig. 3). — Upper pair of cephalic thorns directed 

 upward and slightly outward ; lateral cephalic thorns 2 in number. 

 Apices of wings extending beyond apices of mid tarsi ; abdominal seg- 

 ments each with a girdle of stout thorns; apical segment with 2 stout, 

 tapering terminal thorns. 



Imago. — The elongate shape of the insects, together with their 

 strong posterior legs and peculiar forwardly curved apical wing- 

 venation, makes it a simple matter to identify the species in the field. 

 The flies are usually deep black with contrasting reddish or yellowish 

 color on wings, legs, or abdomen. 



Mydas clavatus is the largest North American dipteron, and all 

 the Mvdaidae recorded from this countrv are of considerable size. 



