158 Mcrriam — Descnption of a New Prairie Dog. 



Cranial Characters. — Compared with C. ludovicianus the skull 

 is broader aud shorter, with shorter nasal bones, postorbital 

 processes, and zygomatic arches; jugals with antero-inferior 

 angle not only thickened to form a triangular plate, but pro- 

 duced downward so as to overhano- and protect from the out- 

 side the fossa beneath ; horizontal part of jugal broader and 

 shorter; ascending arm of jugal much thinner and not forming 

 a noticeable plate between maxillary and lachrymal; audital 

 bulla? larger and more inflated; basi-occipital narrower; frontal 

 shield more concave ; posterior border of inflected angle of man- 

 dible more nearly at right agles to axis of jaw (more squarely 

 truncated) ; dentition less massive ; anterior face of incisors 

 strongly yellow (instead of white or faintly straw-colored) ; upper 

 incisor with an indistinct groove in front of the inner half. 



The length of the nasals equals the distance from the anterior 

 lip of the foramen magnum to the posterior edge of the palate. 

 In ('. ludovicianus the nasals are much longer. 



In cranial characters C. ludovicianus arizonensis of iNIearns, from 

 soutliern Arizona, is in some respects intermediate between true 

 ludovicianus and rncxica.nus, es])eeially in the unusual develo])- 

 ment of the triangular plate of the jugal, size of the audital bullw, 

 and jjreadth of basi-occii)ital. In the other cranial characters 

 here pointed out, C. niexicaaus differs from C. I. arizonensis as 

 much as from C. ludovicianus proper. 



Measure mods of Specimens Collected of Cynomys mexicanus. 



Locality. 



La Ventura, Coahuila, 



Mexico. 

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Date. 



Mar. 24, '91 



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64 



62 



59 



63* 



61 



62 



60 



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59 



^^Type. 



