8 Myron Harm on Sivenk 



sections of apparent phyletic significance, and these may be very 

 properly regarded as subgenera. 



Historically, the first subdivision of Nomada was proposed by 

 Cockerell and Atkins in 1902 {Annals and Magazine of Natural 

 History, series 7, X, pp. 42-46), when the subgenus Micronomada 

 was proposed with a form of Nomada modesta Cresson as the 

 type (var. vegana Ckll.), and the subgenus Hcminomada with 

 Nomada ohliterata Cresson as the type. In 1903 Robertson 

 raised these to the rank of genera and proposed six other new 

 genera, viz., Gnathias with Nomada bclla Cresson as the type, 

 Cephen with Nomada tcxana Cresson as the type, Ccntrias with 

 Nomada erigeronis Robertson as the type, Holonomada with 

 Nomada superba Cresson as the type, Plwr with Nomada integer- 

 rima D. T. {=^ Integra Robertson) as the type and Xanthidiwn 

 with Nomada luteola Olivier as the type ( Canadian Entomologist, 

 XXXV, pp. 172-79). In the same year Cockerell proposed as 

 subgenera Mclanomada with Nomada grindcliac Cockerell as the 

 type and Nomadula with Nomada articulata Smith as the type 

 {Proceedings of the Philadelphia Academy of Natural Sciences, 

 p. 611). 



These several groups fall readily into two general divisions, 

 those with the anterior coxae simple or but feebly spined and 

 those having them rather distinctly or conspicuously spined. Into 

 the former division fall Nomada (sens, str.), Phor, Gnathias, 

 Holonomada, Xanthidium, Heminomada and Melanomada, while 

 into the latter division fall No)uadula, Centrias, Cephen and 

 Micronomada. These two divisions almost deserve generic 

 recognition, yet some species of Nomada sens. str. {e. g., denticu- 

 lata) have distinct though feeble coxal spines, while other 

 species, referable by their characters to Xanthidium (e. g., jennei, 

 mimula, zi'heeleri, etc.), have entirely the habitus of Micronomada 

 and are obviously closely related to the species falling in that 

 group, differing only in the lack of coxal spines, these being in 

 some cases represented by minute coxal tubercles. Evidently, 

 then, these two divisions approach each other too closely to be 

 regarded as distinct genera. 



Melanomada is quite distinct in the unique puncturation of the 



