Marsh Collection, Peabody Museum. 



199 



the type, but in other specimens is similar to the first but 

 larger. There is no internal cusp as in Oxycena. The crown 

 of the fourth is made up of the usual elements found in the 

 typical sectorial premolar, although certain parts are little 

 developed. There are two main external cusps, together with 

 a small but distinct anterior basal cusp ; to these is added a 

 relatively large internal lobe, which is placed opposite or a 

 little anterior to the large principal external cusp. The pos- 

 terior external cusp is proportionally small, and the posterior 



72 



mi 



Figure 72. — Left mandibular ramus of Limnocyon vents Marsh (type of 

 Limnocyon riparius Marsh) ; side view ; three halves natural size. 



border of the main cusp is little produced, so that the 

 shear of this tooth cannot be said to be very perfectly devel- 

 oped. The first molar is the largest tooth of the series ; its 

 crown is composed of two principal external cusps, well sep- 

 arated, a strong blade-like postero-external spur, between which 

 and the postero-external cusp is a deep vertical fissure, a basal 

 antero-external ledge, and a large lunate internal cusp. The 

 large postero-external spur, together with the postero-external 

 cusp, furnish the principal shear, and constitute the chief sec- 

 torial organ of the superior series of teeth. The last molar is 

 relatively large, three-rooted, and trans- 

 verse ; its crown is composed of one 

 main external cusp, external to which, 

 and separated by a slit-like fissure, is a 

 sharp ridge, which has more or less of a 

 sectorial function. The usual internal 

 lunate cusp, together with distinct ante- 

 rior and posterior intermediates, are pres- 

 ent, but the postero-external cusp is ves- 

 tigial or wanting. 



The type of Limnocyon riparius, fig- 

 ures T2, 73, which I take to be the same 



as L. verus, consists of the greater part of both mandibular 

 rami and a portion of a first superior molar. The specimen 



73 



Figure 73. —First molar 

 and fourth premolar of the 

 preceding figure ; inside 

 view ; three halves natural 



