32 PATAGONIAN EXPEDITIONS: PALEONTOLOGY. 



DiADiAPHORUS MAjuscuLUS Ameghino. 



(Plates I; II, Figs, i, la, 2; III, Figs, 4-7; IV; V; XIII, Fig. 9.) 



D. majttsculus Amegh.; Enum. sistematica, etc., 1887, p. 20. 



D. diplinthius Amegh.; Rev. Argent, de Hist. Nat., T. I, 1891, p. 298. 



Bunodonthermm majusctihtm Mercerat ; Revista del Museo de La Plata, 



T. I, 1 89 1, p. 454. 

 B. patagonicum Mercerat; Ibid., p. 453 {fide Ameghino). 

 Oreomeryx Rutimeyeyi Mercerat ; Ibid., p. 469 {fide Ameghino). 



This is by far the commonest and best known representative of the 

 genus and the only one of which any considerable part of the skeleton 

 has been recovered : consequently, the diagnosis of this species, as of the 

 others, must be drawn principally from the teeth. 



In D. majitsctibts the upper caniniform incisor is moderately heavy and 

 is followed by a long diastema. In the upper molars the posterior conule 

 is placed close to the postero-external cusp and separated by a deep cleft 

 from the postero-internal, so that even in well worn teeth the posterior 

 fossa still communicates with the median valley. The postero-external 

 cusp of ml is reduced in size to a degree which varies somewhat in dif- 

 ferent individuals. The development of the internal cingulum on the 

 upper teeth is subject to considerable individual variation and does not 

 afford a trustworthy criterion for the discrimination of species. 



In the lower jaw, the small median incisors are separated by short inter- 

 spaces from each other and from the caniniform laterals, which are quite 

 large and but moderately divergent. The canine is isolated by very short 

 diastemata in front of and behind it and the second premolar has a fore- 

 and-aft position parallel with the axis of the jaw. 



In the following table No. i is a cast of the type specimen of D. diplin- 

 thius ; No. 9291 is a very perfect skull and mandible in the American 

 Museum of Natural History, and No. 9270, of the same collection, com- 

 prises a large part of the skeleton of an old and rather small individual, 

 perhaps a female, while No. 15,799 i^ the most complete skeleton in the 



Princeton Museum. 



Measurements. 



No. No. No. 



No. I. ij,ygg. p^pi. gzjo. 



Upper dentition, length .156 .150 .145 



Upper incisor, antero-posterior diameter . . . .009 .009 



" " transverse diameter .... .007 .007 



