452 



BULLETIN 6.3, UNITED STATES NATIONAL MLTSEUM. 



Conlractuni 

 Glabrum 



Klongatiun 



course either by a faint groove or a distinctly elevated line; it be- 

 comes almost entirely absent in the broadly margined species. In the 

 middle of the series the marginal line of the elytra does not attain 

 the apex {glahrum^ contractum, and platium) ; at the extremes of the 

 series it does. 



In those species with feeble elytral margin the humeral angles are 

 more distinct and even prominent {depi'essum) , and less so as the 

 marg'ins increase. Note again Avhat has already been said relative to 

 the obliquity of the third abdominal segment (see \). 451 and below). 

 Genealogy. — The scheme herewith presented illustrates what has 

 already been said above relative to the apparent progressive ditfer- 

 entiation of the species. 



The two species which form the extremes of the whole series are the 

 most distinct, not only from each other, but from the other members 

 of the same dichotic stem of the ancestral trunk. 



Mvricatun} has the broadest foliaceous margin; the basal angles 



of the pronotal margin project 

 backward over the humeral an- 

 gles of the elytra ; the anterior 

 tibite are not carinate externally. 

 De/pressum, has the narrowest 

 nuirgin ; elytral base more dis- 

 tant from the prothorax, and 

 quite densely sculptured. 



In each hemi-series the mar- 

 ginal line decreases — that is, 

 strongest in murieatxvm^ weakest 

 at apex in contraction ; strongest 

 in depreHsum^ weakest at apex in glahrion. 



It can be assumed that the acquisition of the ()l)rKiuity of the third 

 segment might determine the lines of divergence from the ancestral 

 trunk. 



A careful consideration of tlie diagram in connection with the 

 characters enumerated under the specific lieadings shouhl further 

 elucidate the interesting relationships. 



Dist/ihi/tioii. — Thus far I have studied material from the foUow- 

 ing States and Territories: California, Arizona, Nevada, New Mex- 

 ico, Texas. Colorado, Kansas, Nebraska, AVvoming, and South 

 Dakota. 



It will be observed that Ernbaphion has a large area of distribu- 

 tion — approximately two-thirds of the region west of the Mississippi 

 River, not entei'ing the region west of the Sierra Nevada Mountains, 

 nor the extreme northwestern and northern States. 

 Deprefisam from eastern central California. 

 Eloiigatwni from eastern northern California and western Nevada. 



Depressum 



3rd. Segment Horizantal 3rd. Segment OtKque 



FlU. 8.- 



-GeXEAI.OGICAL DIAGIIA.M OF 

 GENUS EXtBALPHION. 



