OP PHILADELPHIA. 359 



somewhat trilobate : feet yellow; posterior tarsi blackisli : venter 

 yellow, tinged at tip with ferruginous. 



Length one-fourth of an inch. 



Closely allied to S. marginatus nob., but the abdomen is much 

 more elongated. [165] 



3. S. ECTYPUS. — Segments of the tergum edged with yellow 

 and with a lateral oblique line. 



Inhabits Mexico. 



Head yellow : proboscis black : vertex blackish : occiput black : 

 posterior and inferior orbits gray : mouth, each side and beneath 

 black : thorax green-gray, with an obsolete capillary line reflect- 

 ing yellowish : scutel honey-yellow, darker on the middle base : 

 poisers yellow : tergum black, edged all round with yellow ; 

 second segment with two yellow dots ; third and fourth segments 

 with their basal edges and dorsal line yellow, and on each side a 

 wider line originating from the base, and curving a little towards 

 the dorsal line, abbreviated, rounded at tip and tinged with ru- 

 fous ; fifth segment rufous with three black spots : pectus blued- 

 black : feet white : posterior tarsi blackish. 



Length less than one-fifth of an inch. 



ERISTALIS Fabr. Meig. 



E. TRIFASCIATUS. — Thorax grayish, trifasciate ; tergum with 

 a band ; incisures yellow. 



Inhabits Mexico. 



Head white, on the vertex a little olivaceous ; behind dark 

 olive, with white orbits : antennae with the seta naked, and with 

 a spot above on the front elevation of the hypostoma, and mouth 

 each side honey-yellow : thorax gray-olive, with three equidis- 

 tant blackish bands ; middle band as broad as the [ 166] other 

 two together ; posterior band terminal : wings tinged with yel- 

 lowish, particularly in the middle : scutel pale honey-yellow : 

 tergum black ; second segment with a broad honey-yellow band, 

 interrupted in the middle, and with the third and fourth segments 

 bright-yellow on the posterior margin : feet rufous, tibix paler 

 at base ; posterior thighs blackish at base. 



Length over half an inch. 



1829.] 



