228 NOKTH AMERICAN EUMASTACINAE (ORTHOPTERA) 



the relative antiquity of the faunas of the areas inhabited. It 

 seems probable to us that the present distribution of the genus 

 is due to two parallel lines of dispersal extending north from an 

 original center in IMexico, where possibly the two forms, or others 

 very closely related, will be found to intergrade. The absolute 

 lack of Mexican information makes any further theorizing along 

 these lines unwarranted at this time. Another possibility is that 

 Morsea originally occurred in what is now the hot, arid Lower 

 Sonoran Zone, and possibly in the mountains as well, that in- 

 creasing aridity and temperature, with the competition of a new 

 fauna and the elimination or great restriction of its preferred 

 habitat, forced it into its present zonal position. Some slight 

 evidence in support of this hypothesis might be found in the oc- 

 currence of the genus in "islands" within Lower Sonoran con- 

 ditions, as at Roscoe, California, but this might be explained 

 equally well as a downward extension from the adjacent San 

 Gabriel Mountains, where the genus is wideh^ distributed, along 

 the course of the broad Tujunga Wash. 



Considerable difficulty is experienced in determining accurately 

 whether material of this genus is adult. Having no criterion of 

 wing development we are largely forced to use the abdominal ap- 

 pendages as evidence. In the male sex this method is satisfactory, 

 but in the female sex there is difficulty, as the ovipositor jaws 

 and surrounding plates show httle difference in the adult and in 

 the instar preceding maturity. In this sex the general firmer 

 texture of the chitin and absence of shrivelling will usually indi- 

 cate the adult, but occasional specimens are not easity placed. 



Key to Subspecies 

 A. Fastigium of cf, when seen from dorsum, projecting cephalad of cephalic 

 margin of eyes less than one-half of width of fastigium (pi. XII, figs. 12 and 

 13) ; fastigio-facial angle, seen in profile, acute but not in the least concave 

 ventrad.'* Antennae moderately expanded and subspatulate distad. Infra- 

 ocular portion of genae in cT no deeper than one-half depth of eye, in ? 

 equal to two-thirds of depth of ej-e. Lateral lobes of pronotum propor- 

 tionately longer and more shallow. Cerci of d^ proportionately more 

 slender, moderately falcate dist?ad. 



* Occasional females of M. c. californica show a tendency of this sort, but this 

 is apparently merely an individual fluctuation, as thej- are otherwise quite 

 tjijical. 



