350 ON THE EXTINCT MAMMALIA OF 



pressed from without inwardly, and is worn off to a sharp edge and in a sloping 

 manner internally. 



The canine teeth are quite small, but hold the usual position and direction. Their 

 crown is in greater part lost, but the remaining portion indicates that it was laterally 

 compressed and conical. The fang produces comparatively slight prominence of its 

 alveolus on the side of the face. 



Substitute a pair of tubercular molars for the sectorial tooth of the Dog, and we 

 would have almost a likeness of the molar series of Leptictis. 



The first premolar is separated from the canine by an interval of about a line, and 

 an interval of less than half that extent separates it from the second. This and the 

 third are close together, but a small interval separates the latter from the fourth. 



The anterior three premolars, of which the third one is represented magnified 

 three diameters, in figure 28^, plate XXVI, successively increase in size and are 

 inserted by two fangs. Their crown is laterally compressed conical, with the base 

 somewhat extended behind. The third one has its base posteriorly relatively thicker 

 than the others. These teeth have their apex blunted or worn, and they are also 

 worn off posteriorly. 



The four posterior molars are close together, and appear to be inserted by a pair of 

 fangs externally and a lax'ger one internally. Their crowns are nearly alike in form, 

 and the anterior three in size, the last one being the smallest. In the specimen the 

 remaining fifth and the sixth molars of one side are mutilated, and the others are 

 blunted from wearing. 



The crowns of the four posterior molars, of which the first is represented three 

 times the diameter of nature, in figure 28*, resemble in shape those of the tubercular 

 molars of the Dog, and in form and constitution the penultimate tubercular molar of 

 the Ichneumon. They are broader transversely than fore and aft, and project exter- 

 nally beyond the line of the premolars in advance, than which they are also shorter. 

 They are trilateral, and are composed externally of a pair of conical tubercles or 

 lobes bounded by a feeble basal ridge, and internally of a broad crescentoid lobe 

 bounded by a strong basal ridge posteriorly and a feeble one anteriorly. Between 

 the inner and outer lobes the surface is concave, and devoid of the pair of intermedi- 

 ate tubercles existing in the tubercular molars of the Dog and the posterior molars of 

 the Opossum. 



The species of Leptictis is named in honor of Professor F. V. Hayden, who has so 

 zealously explored a great part of the region of the Upper Missouri, and has so 

 efficiently investigated its geology and palasontology. 



The measurements of the skull oi Leptictis Haydeni are as follow: 



