GLIRES OF THE SANTA CRUZ BEDS. 477 



EOCARDIA PETERSONI, sp. nov. 



The type of this species, a left ramus mandibuli (No. 15,323), was found 

 ten miles south of Coy Inlet by Mr. O. A. Peterson, to whom the species 

 is dedicated. It differs markedly from all the other species in the form of 

 the valleys, at least in the lower teeth. In the other species the valley 

 ends internally in a simple, narrow, cement-filled cleft, but in the present 

 species the valley of the lower molars is divided internally into two short, 



divergent branches ; in m T and nw 



& FIG. 49. 



the prominence which separates 

 the branches is symmetrical and 

 placed in the middle of the tooth, 

 but in nig it is asymmetrical and 

 both branches curve forward into 

 the anterior prism. This arrange- 



.. , . Type of Eocardia petersoni, left mandibular 



ment persists for a long time, but ramus> crown view> x f 



eventually wears away, as is evident 



from a comparison of the three molars. The type is from a fully adult, 



rather old animal and p has no indication of the divided valley. The 



outer edges of the prisms of the molars are set off as pillars with quite 



unusual distinctness. 



The mandible is rather short and heavy, with prominent masseteric crest 

 and external border of the masseteric fossa. 



In size E. petersoni agrees closely with E. montana, but is not likely to 

 prove a variation of that species, for none of the specimens of the latter 

 show any tendency to vary in that direction. 



MEASUREMENTS. 



Lower dentition, length 038 P T( length (i. e., antero-posterior diam- 



p^-m, 0175 eter) 0035 



Lower incisor, width 003 P^, width of anterior prism 0025 



" " thickness 0035 Mandible, depth at p ? oio 



EOCARDIA PERFORATA Ameghino. 



(Plates LXVIII, Figs, 23-23" ; LXIX, 2, 2.) 



Eocardia perforata Amegh.; Enumeracion sistem., etc., 1887, p. 13. 

 Eocardia fissa Amegh.; Rev. Argent, de Hist. Nat, T. I, 1891, p. 146. 

 Dicardiafissa Amegh. ; Enum. Synopt des Mamm. Foss. de Patagonie, 

 1894, p. 74. 



