1910.] CJuirac(cr.'< of the Stem Insectivores. 291 



protoconulc, the two together forming the })rotolopli, wliicli connects exter- 

 nally with the paracone. Simihirly the enlarged hyi)oeoiu- unites with the 

 metaconule, which joins the metacone, all forming the metaloi)h. 



(9) Lower mokirs fuberculosectorial, with high trigonid and low talonid. 

 From the widespread occurrence of a well developed talonid in Eocene mam- 

 mals of many orders, and in all Insectivores except the Zalambdodonts, it 

 seems likely that the extremely reduced condition of the talonid and absence 

 of a distinct hypoconid in that group is partly secondary, and perhaps corre- 

 lated with the development of a sectorial rather than crushing function. 

 If this be true the general resemblance of the lower molars of Zalambdodonts 

 to those of certain Jurassic Trituberculates is secondary. 



(10) Denial formula ~^^. This primitive Placental formula is realized 

 among the existing families only in the Gymnurinte, Myogalinfe, Talpinse. 



(11) Milk dentition well developed, not replaced until the animal attains 

 adult size. This is regarded by I^eche as a very primitive mammalian char- 

 acter and possibly may have characterized the ancestral Insectivore (p. 260). 



(12) Cerebrum small, smooth; cerebellum not covered. 



(13) Olfaciory parts large or moderately developed. Possibly the ex- 

 treme macrosmatism of the Zalambdodonts may be a secondary Insectiv- 

 orous adaptation. The large size of the olfactory bulbs in those forms 

 probably conditions in part the peculiar cylindrical development of the skull 

 (p. 267). 



(14) Brain case small, rounded, temporal crests more or less parallel 

 (cf. Ictops, Microgale, Ptilocercus); later uniting into a long low sagittal 

 crest (Zalambdodonts, Pantolestes). 



(15) General architecture of skull much as in Ictops (p. 261). There is 

 considerable evidence (p. 262) that Ictops has retained many primitive condi- 

 tions especially in the base of the cranium and that the ancestral Insectivore 

 was not distinguished either by ectopterygoid fossae, large tympanic flanges 

 on the basisphenoid or united post-glenoid and post-tympanic processes. 

 The malars were probably rather slender. 



(16) "Marsupial" characters in the skull probably fewer than in later 

 Insectivores. Very possibly the palate was not fenestrated, the optic nerve 

 may have pierced the orbitosphenoid (p. 246), one branch of the entocarotid 

 may have entered through the foramen lacerum medium (p. 247), instead of 

 piercing the basisphenoid. 



(17) Venous foramina much as in Solenodon (p. 248). Possibly includ- 

 ing a prominent "sinus canal" on the side of the head, a "transverse canal"' 

 tunneling the basisphenoid, and a suboptic foramen e. g., Solenodon, Erina- 

 ecus, Macroscelides. 



(18) Alisphenaid canal present or in course of development. 



