CALVEET: ODONATA OF PARAGUAY. 29 



5. Trilhemis iinibi*ata Linné. 



Two females, in wliicli the nodal sector is too distinctly waved 

 to enable this character to be used as diagnostic from Dythemis, 

 as I did in Proc. Calif. Acad. Sci. (2) iv, p. 472, 1895. 



6. Trilheinis unimaoiilala De Geer. 



Líbellula unimaculata De Geer, Mém. iii, p. 558, pl. 2(3, f. 5, 

 1773. — Burm., Handb. ii, p. 855, 1839. — Eamb., Névr. p. 

 111, 1842. 



Seven males, of different ages, and one female. Total length cf 

 84-35; abdomen (f 21-22, 9 21; bind-wing (f 27-28, 9 28; pte- 

 rostigma 3-3,5. Front wings witb 10-11 antenodals, 11 occnrring 

 more often; liind wings witb 7 ( 9 )-9 antenodals, 8 occnrring most 

 often. Tbe basalspot on tbe wings is clear brownisb-yellow in tlie 

 yonng males, opaqne brown (almost black) in tbe oldest (^^ruino- 

 se) males: it reaches ont to tbe second antenodal and into (but ne- 

 ver beyond balf of) tbe internal triangle of tbe front wings of tbe 

 males, to the first antenodal and tbe level of tbe arcnlus in tbe fe- 

 male. Ontbe bind wings it reacbes to tbe fourtb or fiftb antenodal 

 and tbe apex of tbe triangle, or even a little beyond tbis latter, in 

 tbe males, wbile in tbe female it attains tbe second antenodal and 

 tbe base of tbe triangle. 



Tbe vértex and tbe npper surface of tbe frons are metallic bine, 

 even in tbe yonng males ; tbe bead of tbe female bas, nnf ortnnate- 

 ly, been lost. 



Only in tbe oldest males do distinct black stripes occnr on tbe 

 tboracic sntnres andtbere aj^pear to be no stripes on tbe meso- and 

 metej^imera. 



Tbe formnla of cells in tbe posttriangnlar field, front wings, is 

 3. 3 or 2. 2. 2. 2. 2 or 3. 2 or 3 5-7. 



Tbese individnals seem to agree perfectly witb De Geer's des- 

 cription and figure. 



Unimaculata belongs to a group of sj)ecies in wbicb tliere is but 

 one row of cells between tbe snbnodal sector and tbe supplemen- 

 tary sector next below", two rows of cells in a part at least of tbe 

 posttriangnlar field of the front wings, and witb tbe superior 

 appendages of tbe males decidedly convex in tbe basal balf, as 



