154 PATAGONIAN EXPEDITIONS: PALEONTOLOGY. 



ADIANTHUS Ameghino. 



Adianthus Amegh.; Rev. Argent, de Hist. Nat, T. I, 1891, p. 134. 

 Adianfus Ar^tgh..; Enum. Synopt, etc., 1894, p. 27. 



This genus is known to me only from the author's descriptions, which 

 are substantially as follows : The third upper molar resembles that of 

 Macrauchenia in miniature, with similar number and arrangement of the 

 enamel lakes, but the external face lacks the mesostyle, which is replaced 

 by a depression. There are two external roots and one internal, the latter 

 very broad. (Ameghino, 'o\b, 52.) 



The mandibular dentition has the formula, \z, Ct, Pt, M3, and the teeth 

 are arranged in continuous series. The lower molars differ from those of 

 Theosodon in having no trace of the spur or pillar in the posterior crescent. 

 The incisors are small and placed in the same longitudinal line as the 

 grinding teeth. The canine resembles the incisors in form and the anterior 

 premolars are like the canine, and the posterior premolars intermediate in 

 character between the anterior premolars and the molars. From the first 

 incisor to the last molar there is a gradual and successive modification of 

 form. The horizontal ramus of the mandible has a straight inferior 

 border and is of nearly uniform dorso-ventral depth throughout. (Ame- 

 ghino, '94a, 27, 28.) 



Adianthus buccatus Ameghino. 



Adianthtts buccatus Amegh.; Rev. Argent, de Hist.^ Nat, T. I, 1891, 



P- 134- 

 Adiantus bticahts Amegh.; Enum. Synopt, etc., 1894, p. 28. 



This is a very small animal, far smaller than any species of Theosodon. 

 The lower dentition is 62 mm. long ; my is 7 and m2- 9 mm. in length, 

 and the horizontal ramus below my is 14 mm. in dorso-ventral depth. 

 (Ameghino, '94a, 28.) 



Localities. — Not given. 



