EDENTATA OF THE SANTA CRUZ BEDS. 



309 



PELECYODON CRISTATUS Ameghino. 



(Plate LII.) 

 Pelecyodon cristatus Amegh. ; Rev. Argent, de Hist. Nat., T. I, 1891, 



P- 323- 

 Pelecyodon robustus Amegh., Ibid. 



This is a very variable species, with a considerable range of difference 

 in size, in the proportions of the teeth, etc., but the individuals grade into 

 one another so completely that it is impracticable to separate them. In the 

 type-specimen - is much compressed laterally, extended antero-posteriorly, 

 forming in cross-section an elongate, very narrow oval ; the grinding sur- 

 face is bevelled to a sharp point by abrasion on both sides ; a second 

 individual, belonging to the La Plata Museum, appears, from the 

 shape of the empty alveolus, to have this 

 tooth of similar form, but somewhat 

 broader transversely ; in other individuals, 

 again, the transverse width of the tooth is 

 greater, the antero-posterior length is less, 

 while the abrasion is only on the posterior 

 side. The second upper tooth is subcylin- 

 drical, varying only in size and in the nar- 

 rowness of the anterior face, which is never 

 so broad as the posterior ; - and - are trans- 

 versely oval and - is very small and may 

 or may not be made reniform by a vertical 

 groove on the posterior face ; in the same 

 specimen this groove may be present in - 

 of one side and not of the other. In the 

 mandibular dentition y is small and long- 

 itudinally elliptical or trihedral ; ? and -j are 

 transversely oval and T is subcylindrical. 



FIG. 37. 



Pelecyodon cristatus. Mandible, 

 crown-view, x \. Amegh. Coll. 



MEASUREMENTS. 



Type, L. P. Museum. No. 15,049. No. 1 



Upper dentition, length 037 .032 .040 .035 



" " " A-A 027 .023 .030 .025 



J-, length (i. e., antero-posterior diameter) 008 .008 .0073 .006 



" width (t. e., transverse diameter) 004 .0045 .0043 .005 



