268 Bulletin A^nericaii Museum of Natured History. [Vol. XXVII, 



Since the common origin of the Centetoidea cand Erinaceoidea seems well 

 assured from the evidence cited on page 266, we must believe that most of the 

 special Centetid characters above enumerated, except possibly the V-shaped 

 protocone of the upper molars, the lack of a hypoconid, and the position of the 

 posterior mental foramen, have been acquired by the Centetidse after they 

 became separated from the forerunners of the Erinaceoidea. 



The date of this separation can at i)resent only be determined within 

 very wide limits. It was certainly not later than the I^ower Eocene, for in 

 the Eocene and Oligocene the family Leptictidse had already become Erina- 

 ceoid in many characters, while by the time of the Lower Oligocene the 

 Zalambdodonts had differentiated into Chrysochlorids (p. 25S) and Centetids 

 {Apternodus, p. 259), the Solenodontidse also possibly being represented by 

 Microftcrnodus (p. 259). 



As to the lower limit for the date of separation there is still less to guide 

 us. If the Potamogale upper molar be more primitive than the Microgale 

 molar then the morphological gap between the Microgale and presumably 

 the Apternodus molar on the one hand and the Ictops molar on the other is 

 very profound and the separate phylogenetic lines representing the Lep- 

 tictidse and the Centetidje would have to be prolonged back very far before 

 they would run together. If on the contrary (as seems on the whole more 

 probable) the Microgale molar is the primitive Centetid type, then the 

 principal ilifi'erence between it and the more primitive Ictops molar lies in 

 the reduction of the paracone and sometimes its fusion with the parastyle. 

 In that case the lower limit for the separation of the Erinaceoids and Cente- 

 toids might perhaps be the Basal Eocene or Upper Cretaceous. 



Solenodontidoe. The analysis of the characters of Solenodon paradoxus 

 given on pages 253-255 fully supports the view that this family belongs in the 

 Zalambdodonta and has only a subordinal relationship with Myogale, which 

 resembles it in several homoplastic characters in the skull and incisors. 



In several characters {e. g., retention of postorbital constriction, a sub- 

 optic canal communicating with the presphenoid sinus, absence of tympanic 

 wing on basisphenoid, form and relations of petrosal) Solenodon resembles 

 either Ictops or the Erinaceidse rather than the Centetidae, and the resulting 

 suggestion is that the Solenodontidai have been derived, not from any early 

 Madagascan Centetids but from some more generalized Holarctic Zalamb- 

 dodonts, such as Micropternodus of the American Oligocene (p. 259). 



The Menotyphla. 



The group including the families Tupaiidse and Macroscelididre appear 

 to be very widely removed from the other Insectivora, so far, in fact, that it 



