616 INSECTIVORA 



line of descent. The deeply pectinated crowns of the lower incisors 

 of Galeojnthecus are quite unique in the class, and the only approach 

 to the double-rooted canine, except in Erinaceus and Talpa, is found 

 among the Marsupials in Perameles, where the root of the canine is 

 grooved. 



Suborder Ixsectivora Vera. 



Upper and lower incisors conical, unicuspidate or with basal 

 cusps only, the lower not pectinated ; limbs free, formed for 

 terrestrial progression. 



The following table gives a key to the distinctive characters of 

 the existing families : — 



I. Upper molars broad, multicuspidate, with more or less well-defined 



"\V-shaped crowns. 



A. Symphysis pubis long ; generally a csecuni ; cerebral cavity 



comparatively large. 



a. Orbit encircled by bone ; metatarsus moderate ; arboreal. 



Tupaiidce. 



b. Orbit not encircled by bone ; metatarsus greatly elongated ; 



terrestrial. Macroscelididce. 



B. Symphysis pubis short or none ; no ccecum ; cerebral cavity 



small ; skull without postorbital processes. 

 a. First and second upper molars with a central fifth cusp. 

 a. Tympanic annular, not forming a bulla. Erinaceidw. 

 h. No central fifth cusp to upper molars. 



«'. Tympanic annular, not forming a bulla ; no zygomatic 



arch. Soricidce. 

 b'. Tympanic forming a bulla ; zygomatic arch developed. 

 Talpidce. 



II. Upper molars narrow, with V-shaped crowns. 



a! Tympanic annular, not forming a bulla ; zygomatic arch 

 imperfect, 

 a". No clavicles. Potamogalidm. 

 b". Clavicles well developed. 



a". Skull constricted between the orbits ; penis sus- 

 pended. Solenodontida'. 

 b'". Skull not constricted ; penis pendent, retractile. 

 Centetidce. 

 b'. Tympanic forming a bulla ; zygomatic arch well developed. 

 Chrysoehloridn . 



The second section, in which the molars are of the primitive 

 tritubercular type, should probably be regarded as containing the 

 most generalised representatives of the order ; and it is noteworthy 

 that the whole of them are confined to Africa, Madagascar, and 

 the West Indies, whereas most of the first section are widely 

 distributed over the Paloearctic and Oriental regions. None of the 



