MOUNTAIN ANTS OF NORTH AMERICAN. 513 



Colorado: Boulder (P. J. Schmitt and W. W. Robbins). 



South Dakota and Utah: (Emery). 



Michigan: Washington Harbor, Isle Royale (O. McCreary). 



At Glacier and Lake Louise I found several colonies of this ant 

 nesting under stones in rather damp places. The worker form, origi- 

 nally described from South Dakota, Utah and Colorado, differs from 

 the typical canadensis and the preceding varieties in its somewhat 

 finer sculpture and paler color, the mandibles, antennae, except their 

 clubs, the thorax, pedicel and legs being reddish brown or red, the 

 femora infuscated in the middle. The epinotal spines are rather long 

 and pointed. The male measures 4 mm. and is distinctly larger than 

 the worker (2.5-3 mm.) and only slightly smaller than the typical 

 acervoruDi, from which it is almost indistinguishable. Comparison 

 with Swiss specimens shows that the American variety has a darker 

 pterostigma and smaller epinotal protuberances. The female is 

 somewhat smaller and darker than the female of the typical acervorum. 



50. Leptothorax (Mychothorax) acervorum subsp. canadensis var. 

 calderoni Forel. 



I have taken numerous workers and females of this form in the 

 type locality (about Lake Tahoe, Cala.), where it is common in little 

 nests in the bark of large pine logs and stumps, often in plesiobiosis 

 with Camponotus herculeanus var. modoc. The worker has the color 

 of the var. yankee. According to Forel the antennal scapes are longer 

 than in canadensis, reaching nearly to the posterior corners of the head, 

 but my specimens show considerable variation in this particular. 

 Nor do I find that the worker calderoni is larger than the European 

 acervorum, though it is larger than the var. yankee. My workers vary 

 considerably in size, from 2.5-3.5 mm. The main difference which I 

 detect between yankee and calderoni is in the proportions of the pro- 

 mesonotum, the length of this region in the latter form between the 

 cervical ridge of the pronotum and the mesoepinotal suture being more 

 than 1§ times the breadth of the pronotum through the humeri, 

 whereas in yankee it is distinctly less. Sculpture and pilosity are 

 very similar in the two forms. 



5L Leptothorax {Mychothorax) acervorum subsp. crassipilis subsp. 

 nov. 



Worker. Length: 2.5-3 mm. 



Differing conspicuously from the preceding forms of acervorum in 

 sculpture and pilosity. The surface of the head, thorax, petiole and 



