242 ON THE EXTINCT MAMMALIA OF 



Among a large number of molars from diflFerent parts of the United States, pre- 

 served in the Museum of the Academy of Natural Sciences, two varieties may be 

 observed, but with all shades of gradation between those which appear most distinct. 



Smooth variety of teeth are distinguished by the comparatively regular transverse 

 angular lobes of the crown, separated by as regular transverse angular valleys, hardly 

 obstructed in their course by any projection from the bounding lobes. The sides of 

 the latter slope regularly and smoothly, but the outer lobes of the lower teeth, and 

 the inner ones of the upper teeth, present a more or less well-developed buttress-like 

 ridge, projecting fore and aft into the transverse valleys. The enamel is compara- 

 tively smooth; the basal ridge slightly developed. 



In the rugged variety of teeth the lobes of the crown are more rounded or less 

 sharply angular, and the transverse valleys are more or less obstructed by a greater 

 degree of development of the buttress-like projections of the outer lobes of the lower 

 teeth, and of the inner ones in the upper teeth. The sloping sides of the valleys are 

 more or less strongly wrinkled and tuberculate, looking like the slopes of hills 

 washed into grooves by rains. The enamel is generally more or less rugose, and the 

 basal ridge well developed and rugged. 



In the smoother variety of teeth the last molars are more uniform in transverse 

 diameter than in the other variety. In this they appear to have a greater tendency 

 to prolongation and narrowing behind, as well also as to have a disposition to- increase 

 in the number of transverse lobes. 



The rugged variety of teeth approach more nearly than the others those o^ Masto- 

 don andium. 



Mastodon ? — The Mastodon tooth, previously mentioned as having been 



obtained at Tambla, Honduras, is a nearly perfect last upper molar of the left side. 

 Tambla is a village in one of the passes leading from the plain of Comayagua to the 

 Pacific. In the same locality Dr. Le Conte detected remains of a species of Bas and 

 Equus* Fragments of teeth of the latter, presented to the Academy, indicate an 

 animal about the size of the Ass, but are too imperfect to characterize the species to 

 which they pertain. 



The Tambla Mastodon tooth, represented in figure 14, plate XXYII, resembles so 

 nearly a corresponding one from Tarija, Bolivia, described and figured by M. Gervais in 

 his Recherches sur les Mammiferes Fossiles de I'Amerique Meridionale,-]- page 20, plate 

 5, figure 3, and referred by him to the Mastodon andium, that the specimen may be 

 viewed as belonging to the same species. It is smaller, as Gervais gives eighteen 

 centimetres for the breadth fore and aft, and nine centimetres for the width in front 



* Proc. Acad. Nat. Sci. 1858, 7. 



t Forming part of the Zoologie de I'Expedition dans les parties centrales de I'Amerique du Sud de M. le 

 Comte F. de Castelnau. 



