352 ON THE EXTINCT MAMMALIA OF 



The remains of the molar teeth in the specimen ak)ne serve to distingiiisli. lliis 

 fossil from Lepliclls. They also apparently indicate the insectivorous nature of the 

 animal. The portions of teeth remaining are tliose of the back six molars on one 

 side and five on the other, except the last one. 



The second premolar is two-fanged as in Leptidis, and its crown, which is lost, 

 appears to have had the same form as in the latter. 



The third premolar in Leptictis has the same form and construction as that in ad- 

 vance, but in Ictops, the name by which we designate the genus to which we have 

 referred the fossil under examination, it is very different. In this it is inserted by 

 three fangs, two external and one internal. The crown, as represented in the 

 magnified view, figure 29', is trihedral, and about as wide transversely as antero- 

 posteriorly. It is composed of three principal lobes, two external, the third internal. 

 The outer pair of lobes are laterally compressed conical and connate, with perhaps 

 the exception of the apices, which are broken away in the specimen. In front of the 

 base of the anterior lobe there projects a small pointed tubercle. The inner lobe is 

 a trihedral pyramid nearly median in position in its relation with the outer pair, 

 which it conjoins at base. The outer surface is concave, and separated from the 

 inner ones by acute ridges diverging from the pointed summit. A narrow basal 

 ridge bounds the internal lobe posteriorly. 



The four back molars of Idops have the same relative position and size as regards 

 one another as in Leptictis. They, however, do not project abruptly beyond the pre- 

 molars externally as in the latter, as noticed by comparing the relative position of 

 the molars and third premolar of the two animals in figures 28 and 29. 



In the first and best preserved of the four back molars of Ictops, figure 29*, the 

 outer part of the crowii is constructed like that in the premolar in advance, but is 

 slightly more robust, though not quite so wide fore and aft. The pointed tubercle 

 in front is also rather larger, and a more marked basal ridge exists behind. The 

 inner part of the crown is formed of a three-sided pyramidal lobe, proportionately 

 much larger than that of the tooth in advance. The acute borders of this lobe near 

 the middle of their course project into a pair of cusps, which appear as the summits 

 of rudimental lobes springing from the former. Posteriorly the internal lobe of the 

 crown is bounded by a low accessory lobe, which corresponds with the narrow basal 

 ridge in the tooth in advance. A feeble basal ridge also exists at the fore part of the 

 intei'nal lobe of the crown. 



The succeeding tooth, represented in figure 29^, appears to have had nearly the 

 same form as the one just described, but the basal ridge in front of the internal lobe 

 is much better developed. 



The remaining inner part of the crowns of the last two molars appax'ently indicate 

 these teeth to have had the same character as the one just described. 



