88 PROCEEDINGS OF THE ACADEMY OF [1896. 



(2). Median and lateral upward extensions of yellow on face not 

 truncate, or lateral ones notched and subtruncate ; anterior 

 and middle tibise all yellow ; pleura without a large yellow 

 patch ; bauds of abdomen not united (or only the first two 

 or three united) at sides; lower part of cheeks very nar- 

 rowly yellow =niiidella S . 



From biparticeps it is thus distinguished : 



(1). Size smaller, abdomen suffused ; pleura without yellow patch, 



== biparticeps $ . 



(2). Size larger, abdomen not suffused ; pleura with a large yellow 



patch : median face-marks more developed above antennae, 



= maculipes S . 

 It is very much like gutierrezice, but differs from that in its longer 

 marginal cell, the abdominal bands joined laterally, and the upper 

 margin of the yellow of face much more distinctly trifid, besides the 

 marks on the tibia?. It resembles fjutierrezicB in the broadly yellow 

 lower part of cheeks, and the yellow blotch on pleura. 



From small examples of $ bigelovice it is distinguished by the 

 abdominal bands being united at the sides, the fiice-markings as 

 already mentioned, and the tibiae with dark marks — though the 

 middle tibite of bigelovice sometimes show a small spot. The mar- 

 ginal cell is as in bigelovice. 



Hab. — Las Cruces, N. M., one example on Big loviawrightii, Sept. 

 5, 1895. (A.M.Holt.) The above form allies itself very closely 

 with bigelovice and gutierrezice, which have the cheeks more or less 

 broadly yellow and the yellow patch on the pleura. The more one 

 studies these forms the more apparent does it become that nitidellay 

 with its dark pleura and narrow yellow line only on the cheeks, is 

 distinct ; while bigelovice, gutierrezice and maculipes run each other so 

 close that they seem to be varieties of one species. Yet I leave them 

 as they stand, not because I think that they are what would be called 

 good species, but rather to draw attention to the divergence which 

 may represent an early stage in species-formation. It will be noted 

 that mactdipes, while retaining the essential characters of bigelovice, 

 departs in its face-markings toward the condition of nitidella. 



50. Perdita pellucida n. sp. 



$ . — Length about 5 mm. Head very dark blue, thorax black 

 except the dark blue metathorax. Head of ordinary size, rounded, 

 broader than long; cheeks unarmed, mandibles moderately stout, 

 simple. Vertex granular. Face with rather conspicuous but very 



