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than in that species. There arc two anterior outlets of the dental canal, one beneath p i, 

 the other beneath the socket of /; 2. The outer alveolar wall descends at once from the 

 sockets to the outward swelling of the ramus, two thirds down toward the thick rounded 

 lower border of this part of the mandible. The angle at which the symphysial end seems 

 to rise from the lower border resembles that in Triconodon mordax. 



The subject of PI. IV, fig. 4, nat. size, is a portion of a left mandibular ramus, with the 

 inner surface exposed, showing the symphysis and the broken bases of the third or fourth 

 premolars. The faint linear groove along the inner part of the thick under border of the 

 ramus does not answer to that called 'mylohyoid' in fig. 11, PI. Ill; it may be a trace of 

 the line of confluence of the osseous encasing of the primitive mandibular cartilage. But 

 the mammalian unity of the bone is well exemplified in this portion of jaw. 



The extent, shape, and the angle of the long axis of the symphysial surface with that 

 of the horizontal ramus, are the same as in Triconodon mordax (PI. Ill, figs. 7 and 10). 



Species 2. — Triconodon ferox, Ow. Plate III, figs. 11, 12, 13, 17, 18, 19. Plate IV, 



fig. 1. 



The size of the specimen about to be described might be deemed to represent that of 

 the jaw of a full-grown Triconodon mordax, admitting the evidence of immaturity shown 

 by the type-specimen (fig. 7). But although the jaw-bone would grow and bring into 

 view the three main cones and hinder talon of the last molar clear of the coronoid process, 

 yet the crowns of the teeth, once completed, do not grow. Now, the extent of the three 

 molars in situ in the subject of PI. Ill, fig. 11, nat. size, exceeds that of the same teeth in 

 fig. 7 by two millimeters or one line. The extent of the whole molary series in Triconodon 

 mordax is nine lines, in the present jaw it is ten and a half lines. 



Does this indicate a mere sexual superiority of size ? 



It is certain that the molars of the female Tliylacinus are smaller than those of the 

 male, concomitantly with her general inferiority of size. I should be unwilling, seeing 

 the general conformity of the dentition in the present and preceding specimens, to refer 

 the subject of fig. 11 to a distinct species, believing rather that it might represent a male 

 of Triconodon mordax, were it not for the difference in the shape of the mandibular ramus 

 itself, to which I shall next ask attention, the present specimen agreeing more closely 

 in this respect with Phascolotherium than with Triconodon mordax. 



There is, however, an important character in which the agreement with the smaller 

 species of Triconodon is closer, and which may be a generic feature. 



Among existing mammals with a dentition for animal food certain marsupials, e. g. 

 Thyl acinus, Sarcophilus, have the articular condyle of the mandible on as low a level as the 

 alveolar tract. This character is repeated in the Phascolotherium of the Stonesfield 



