388 



FSl 



t 



[September, 1902 



ever, from this species in possessing 

 epinotal spines and smooth posterior 

 corners to the head and from this and 

 all other described North American 

 species in the very dense and delicate 

 cephalic rugae. 



J". desertoi-H7n inhabits the dry stony 

 soil above the flood marks of the streams 

 on tlie canon sides where there are only 

 a few xerophytic shrubs like Fouqiiicra 

 splcndcns ,Jatropha spatJiulata^ Coiidalia 

 mexkana, Larrea mexicaiia, and Flour- 

 cjisia ccniiia. In the open sun-lit spaces 

 among these shrubs the ants make soli- 

 tary mounds 4-6 inches across and per- 

 forated in the centre with an entrance 

 about ^ inch in diameter. They 

 feed on the seeds of a coarse, tufted 

 grass {Muiiroa sp.) which is found 

 growing sparsely near the nests. After 

 the diminutive seeds are removed from 

 the relatively voluminous chaff, the latter 

 is deposited by the ants on the mound 

 immediately around the entrance of the 

 nest. Occasionally the new species 

 builds its nests under single or clustered 

 stones like P. imberbicuhts Wheeler.* 

 None of the nests contained more than a 

 dozen workers, but the weather was very 

 cold and dry and the bulk of the colony 

 may have been hibernating at some in- 

 accessible depth in the stony soil. There 

 can be no doubt, however, that the colo- 

 nies of this species are very much smaller 

 than those of P. barbatus and P. occi- 

 dcntalis. 



*This habit is perhaps only exceptional with iviberbicu- 

 Ins, for I have recently seen these ants building neat little 

 mound nests 3-4 inches in diameter in the dry stony bluffs 

 along the Concho River at San Angelo, Texas. 



POGONOMYRMEX SANCTI-HYACINTHl, Sp. nOV. 



Worker. Length 7.5-9. mm. 



Head rectangular, exclusive of the 7- 

 tootlied mandibles as broad as long ; posterior 

 margin straight. Anterior border of clvpeus 

 with a deep, broad, almost semicircular ex- 

 cision. Frontal area triangular, distinctly 

 longer than broad, convex but scarcely car- 

 inulate in the middle. Eye in the middle of 

 the lateral surface of the head. Tip of an- 

 tennal scape reaching to midway between the 

 e^e and the posterior angle of the head. 

 Thorax shaped like that of P. barbatus but 

 without epinotal spines, their position being 

 indicated in some specimens by a pair of 

 rather short indistinct ridges or projections. 

 Petiole short, the node longer than the 

 peduncle and inuch lower and blunter than in 

 barbatus, the anterior ascending and posterior 

 descending dorsal surfaces of about equal 

 length, the former slightly concave in profile 

 but not distinctly angular as in barbatus, the 

 latter depressed in front and slightly concave 

 behind. Tooth on the ventral surface of 

 petiole obsolescent. Postpetiole campan- 

 ulate, slightly longer than broad, evenly con- 

 vex above, its ventral protuberance very 

 slightly developed as compared with bar- 

 batus. Gaster and legs of the usual ap- 

 pearance. 



Mandibles shining, coarsely and deeply 

 striated. Frontal area opaque. Front and 

 sides of head covered with numerous, paral- 

 lel, clean-cut rugae and with small piliger- 

 ous punctures. The rugae are somewhat finer 

 than those of barbatus and scarcely diverging 

 except on the extreme posterior portion of 

 the head. Interrugal sculpture indistinct, 

 consisting of very shallow, confluent fovetr- 

 lae. On the posterior angles the rugae are 

 replaced by a delicate reticulation and this 

 disappears to leave the corners of the head 

 smooth and shining. Thoracic sculpture 

 like that of the typical barbatus but some- 

 what finer, the prevailing directions of the 

 rugae being transverse on the pro- and 

 epinotuiTi and longitudinal on the mesonotum 



