472 BULLETIN UNITED STATES GEOLOGICAL SURVEY. [Tol.Y. 



B. Three submarginal cells, the third longer than broad, and much 

 narrowed towards the marginal. 



Melissodes Latr. 



Type: Melissodes rustica (Say) Smith. 



Maxillary pal2n four-jointed, the fourth joint often minute; first joint 

 of the labial palpi twice as long as the second ; labrum rounded ante- 

 riorly and either notched, sinuate, truncate (in some males), or entire 

 {himaculata S 9)-, clypeus rarely elevated (desponsa) ; mandibles entire 

 at the tip (in <? desponsa notched) ; antennse of the male as long as the 

 thorax [texana) or longer; inner claw of the i^osterior tarsi of the male 

 longer than the outer claw and its tooth often smaller (in desponsa the 

 claws alike) ; claws of the four posterior tarsi in the female armed with 

 a short, stout tooth which is nearly parallel to the claw ; two apical seg- 

 ments of the male abdomen armed Avith lateral teeth ; enclosure on the 

 seventh segment of the male of moderate width, notched on each side 

 just before the tip ; externo-medial nervure of the anterior wings ob- 

 liquely, not abruptly, bent back just beyond the origin of the first re- 

 current nervure ; basal lobe of the posterior wings extending nearly to 

 the ai)ex of the submedial cell ; scopa of the posterior legs in the female 

 long, dense, and plumose or matted. 



The temale of this genus may be easily distinguished by the great 

 size of the pollen-brush, which somewhat resembles that of JDiadasia. 



Tetealonia Spin. 



Syii. Maerocera Latr. from Spin. MSS. (nee Meigen). 

 Type: Maerocera antennata (Latr.). 



Maxillary palpi fve-jointed; mandibles entire at the tip. It is i3roba- 

 ble that the genus presents the following characters also : bend of the 

 externo-medial nervure not abrupt; basal lobe of x^osterior wings ex- 

 tending to the middle of the submedial cell ; scojm on posterior tihice 

 in the female long and dense ; labrum notched. 



Latreille, who first described Tetralonia (under the preoccupied name 

 Maerocera), states that the maxillary palpi are five-jointed.* A new 

 name becomes necessary for those species with six joints in the maxil- 

 lary palpi, notwithstanding that both Lepeletier and Smith have given 

 the latter character to Tetralonia; for Si)inola, in changing the name 

 Maerocera to Tetralonia, gave no description of the genus, but adopted 

 it from Latreille as it stood. 



* But ill the Voyage de Humboldt ct Bonpland ; Ohserv. de Zool.et d'An. Comp. vol. i, 

 p. 283 (1811), Latreille mentions the genus Maerocera with the single species M. 

 antennata Spin., and gives the following generic characters: "Palpes maxiUaires 

 n'ayant que cinq articles distincts ; le sixieme presque nue on i^eu ai)j)arent. (Trois 

 cellules sous-margiuales.)" In the Encycl. Meth. (1825), the genus is quoted from La- 

 treille's Xouv, Diction. dUiist. nat. 2** Mit. 



