186 BULLETIN 63, UNITED STATES NATIONAL MUSEUM. 



Genealogy. — The accompanying diagram will give my idea of the 

 relationships of the species. It will be observed that from the an- 

 cestral trunk divergence probably occurred along two lines — («) one 

 where the prothorax acquired acute margins, and consequently a con- 

 cave disc; at the same time the spurs underwent but slight ditieren- 

 tiation, and as a result, in the course of time there were produced 

 forms, which being plastic to a moderate extent, became capable of 

 being recognized as a series, the heterotypes of which are our suturalis 

 and texana. These two races are united by true mesotypes. 



{h) The other line of divergence resulted in a less differentiation 

 of the dorsal body w^all, but a greater change occurred in the tibial 

 spurs. Here the dichotomous changes resulted in the present acuta 

 with less calcarine development and ohscura where the tibial calcars 

 are the most differentiated. It appears as if acuta has reacted less 

 to modifying factors, while ohscura has gradually been the most re- 

 active as evidenced by the recog- 

 *"^^ suicipenms ulzable Taccs ,' the lietcrotypes bejug 



/united by an unbroken line of 



<^ mesotypes, 



- \ X ■- \wspersa ^o lu thc liucal arrangement of 



IVoftoraxConcave >| Proftorax Convex ^ ., • 1 i.1 • A'C 4^ " 



acute TOM-gms. spurs I disparity betwe«i anterior tile SDecios aud their iiiodihcations 



iese differentiated I tflaal spurs - t • i i • i i • 



I two distinct breaks m the chain 



Fin. 8.— Genealogical diagram of the are noticeable : First, suturalis and 



OBScuiiA Group. Subgenus Eleodes. ^^„^^^^ ^^,^ distinctly defined specieS 



as regards each other; second, acuta and sulcipennis {ohscura) while 

 less divergent in structure are not united by any known mesotyijes, 

 the heterotypes of acuta more likely only simulate ohscura on the one 

 hand and texana on the other. These are only suggestions, for no one 

 can be sufficiently positive to assume the true relationships of forces 

 that bring about such interesting forms. 



I also wish to call attention to another fact : In dispersa the tarsal 

 grooves of the tibite are the most strongly develojjed, and the articular 

 cavities open the most widely into them, and these characters gradu- 

 ally diminish so that in sutu.ralis they are found at their minimum 

 in the present group. 



By the open articular cavities — the floors of which are directly con- 

 tinuous with those of the tibial grooves, both being on the same plane 

 in the most strongly differentiated examples — greater functional 

 power is given to the tarsi, i. e., they must be more strongly extensible 

 and capable of being more strongly brought into juxtaposition to the 

 tibial surface. 



Distrlhution. — As known to me the present group is distributed 

 through the following 15 States: Texas, New Mexico, Arizona, Kan- 

 sas, Colorado, Utah, Nevada, northern California, Oregon, Washing- 

 ton, Idaho, Wyoming, Nebraska, southern Dakota, and Oklahoma. 



