706 Bulletin American JShiseuni of Natural History. [Vol. XXIII, 



whereas in the typical form there are two or three times as many. Owing 

 to their feebler sculpture the workers of chisosensis are throughout much 

 more shining than the typical form. 



5. Atta (Trachymyrmex) septentrionalis McCook. 



"f CEcodoma virginiana Buckley, Proc. Ent. Soc. Phila., VI, 1867, p. 346, no. 61, $. 

 f.CEcodoma tardigrada Buckley, Proc. Ent. Soc. Phila., VI, 1867, p. 349, no. 65, 0. 



9 (^. 

 Atta septentrionalis McCook, Proc. Acad. Nat. Sci. Phila., 1880, pp. 359-363, Fig. $ . 

 Atta {Acromyrmex) tardigrada Forel, Bull. Soc. Vaud. Sci. Nat. (2) XX, p. 91, 1884, 



p. 358, 9c?. 

 Atta tardigrada Mayr, Verh. zool. hot. Ges. Wien, XXXVI, 1886, p. 442. 

 Atta (Trachymyrmex) tardigrada Forel, Ann. Soc. Ent. Belg., XXXVII, 1893, p. 



601. 

 Atta tardigrada Dalla Torre, Catalog. Hymen., VII, 1893, p. 154. 

 Atta tardigrada var. septentrionalis, Catalog. Hymen., VII, 1893, p. 154. 

 Atta {Trachymyrmex) tardigrada Emery, Zool. Jahrb., Abth. f. Syst., VIII, 1894, 



p. 329. 

 Atta (Trachymyrmex) tardigrada Forel, Rivista Sci. Biol., II, 1900, p. 9. 

 Atta (Trachymyrmex) tardigrada Forel, Ann. Soc. Ent. Belg., XLV, pp. 396, 397. 

 Atta (Trachymyrmex) septentrionalis Wheeler, Trans. Tex. Acad. Sci., IV, Pt. II, 



no. 2, 1902, pp. 13, 14. 

 Atta (Trachymyrjnex) septentrionalis Wheeler, Psyche, June, 1903, p. 101, Fig. 



6b. 

 Atta (Trachymyrmex) septentrionalis Wheeler, Bull. Am. Mus. Nat. Hist., XXI, 



1905, pp. 386, 387. 



Worker. (PI. XLIX, Fig. 4.) Length: 2.5-3 mm. 



Head, without the mandibles, about as broad as long, a little broader behind 

 than in front, with obtusely excised posterior border, somewhat rounded posterior 

 angles and rather straight sides. Eyes not veiy prominent, more than J the distance 

 from the anterior to the posterior corners of the head. Mandibles with two larger 

 acute apical and 7 or 8 small basal teeth. Anterior border of clypeus sinuately 

 excised in the middle. Frontal area triangular, obsolescent. Frontal carinse with 

 flattened, rounded lobes in front, continued back as a pair of diverging ridges beyond 

 the middle of the head as far as but not meeting the lateral carinje. Antennal 

 scapes extending about I their length beyond the posterior corners of the head, some- 

 what thickened towards their tips. Region between the frontal carinse and posterior 

 corners of the head covered with small acute tubercles, one pair of which on the 

 posterior corners is longer and bidentate. Pronotum with a pair of blunt, down- 

 wardly directed inferior spines, two long acute superior spines and between these in 

 the middle a pair of short bidentate spines or tubercles, which are closer to each 

 other than to the lateral tubercles. Mesonotum with two pairs of blunt spines. 

 Mesoepinotal constriction pronounced. Epinotum with four longitudinal rows of 

 tubercles, the inner continued back into the bases of a pair of acute spines which 

 are directed upward, backward and outward and are from J to | as long as the 

 slightly convex base of the eiDinotum. Declivity sloping, forming in profile an ob- 



