JAMES CHESTER BRADLEY 
249 
A Key to the Subgenera 
Males 
1. Rs opposite the radial cross-vein; cell Rs triangular, no longer than cell 
R4 (figure 2); pygidial segment toward the apex with a deep longitudinal 
furrow, making it appear as though divided into two lobes, the apex 
lobed; first ventral segment armed with a recurved hook, the second with 
a tubercle or hook at base; clypeus flat, with a longitudinal median keel 
below the antennae Myrmosa Latreille 
Rs far apicad of the radial cross-vein; cell Rs not triangular, longer than 
cell R4 (figure 1); pygidial segment tapering to the almost acute, very 
slight^ notched apex, without a longitudinal impression; first and second 
ventral segments simple; clypeus convex, without a keel. 
Myrmosula new subgenus 
Females 
In this sex no division of the genus is known, the species are 
therefore all recorded under the t3'pical subgenus Myrmosa 
Latreille. 
A Key to the Species of the Subgenus Myrmosa known to 
OCCUR IN America north of Mexico 
Males 
Pubescence white. (Eastern.) unicolor Say 
Pubescence black. (Californian.) species non descripta 
Females 
1. Anterior half of the second dorsal segment closety punctured (2)“ 
Anterior half of the second dorsal segment polished and shining, with only 
few and scattered punctures. Length 3 to o mm banks! new species 
2. Basal abdominal segment with a transverse dorsal carina; posterior meta- 
tarsi with prominent spines; posterior tibiae with two or three rows of 
ver>^ prominent spines. Length 6 to 8 mm unicolor Say 
Basal abdominal segment without such a carina; posterior metatarsi 
without noticeable spines (there are a few largely hidden by pubescence) j 
posterior tibiae with fewer spines, these small and inconspicuous. Length 
4 mm blakei new species 
Myrmosa (Myrmosa) unicolor Say, d', 9. 
1886. Mutilla thoracica Blake, Trans. Amer. Ent. Soc., 13 : 204, 9 . 
Professor IVIelander is doubtless correct in associating thoracica 
with iinicolor. He remarks upon the occurrence of the females 
in gravel pits among the numerous burrows of Halidas, and my 
own specimens come from exaetty similar situations. 
TRANS. AM. ENT. SOC., XLIII. 
