ORDINAL TYPES OF MOLARS : INSECTIVORA 125 



in which the protocone is large, the paracone and inetacone are 

 widely separated, and the external styles are nearly equal in size. 

 The mesostyle is much reduced in Scotophilus and is drawn inward, 

 the paracone and inetacone are more closely oppressed and the protocols 

 is somewhat shortened. In Harpiocephcdm * the mesostyle has dis- 

 appeared, the parastyle and metastyle have drawn closer together ami 

 compose the entire outer portion of the crown, while the paracone and 

 inetacone are closely approximated, forming the greater part of the 

 inner portion of the crown, the protocone being very much reduced. 

 Thus in Harpioceplialus a stage is reached nearly analogous to that of 

 Potamogale, the principal difference being that the inetacone is the 

 dominant cusp instead of the paracone, as in the latter genus. 



' From these comparisons it seems reasonably clear that such forms 

 as Oentetes, Ericulus and Chrysochloris have attained a secondary or 

 pseudo-tritubercular form by passing through some such stages of 

 evolution as are suggested by the two series here selected. Other 

 examples of a fusing paracone and inetacone and reducing protocone 

 may be found in the molars of some of the creodonts and carnivorous 

 marsupials and in the sectorials of many of the carnivores. 



' From the foregoing it now seems to be demonstrated beyond question 

 that the main inner cone of Centetes and Ericulus is not the protocone 

 as observed in normal groups, but, if not entirely made up of the 

 primary cusp (paracone), it at least involves that element, and 

 Woodward's contention that the evidence of embryology is in entire 

 harmony for the molars and preniolars is not controverted by these 

 seeming exceptions as supposed by Osborn." 



Homologies. The reasons the cusps of the superior molar teeth 

 of Insectivora are difficult to homologize are: (1) that in certain types 

 the strong development of the styles on the external cingulimi tends 

 to confusion with the paracone and metacone, as also in the case of 

 certain Cretaceous mammals (e.g. Didelphops, Figs. 47, F, E], of certain 

 Amblypoda (e.g. Coryphodon, Fig. 141), and in Marsupials (Figs. 58, 59); 

 (j!) the strong development of the paracone in certain types tends 

 to confusion with the protocone; (3) in order to secure a greater 

 number of sharp piercing cusps the mesostyle divides t into two 



1 "The skull of Harpiocephai .$ from which this description was taken was obtained by 

 Mr. G. S. Miller through the kindness of Oldfielcl Thomas, of the British Museum. 



Unfortunately it came too late to be photographed and figured uniformly with the 

 series. Its place is taken on Plate III., by an outline drawing from a figure for Wilhelm 

 Peters' Fledermause des Berlines Museums fiir Naturkunde (a projected monograph of 

 the bats)." 



* [Gidley, J. W., "Evidence bearing on Tooth Cusp Development," Proc. Waxhhif/ton 

 Acad. Sci., Vol. VIII. , 1906, pp. 93-95.] 



t [In certain Marsupials and Insectivores the presence of two distinct mesostyles may be 

 a primitive character. ED.] 



