236 Bulletin American Museum, of Natural History. [Vol. XXVII, 



are structurally allied to the Insectivora on the one hand and to the INIioclfe- 

 nidpe and other primitive Placentals on the other. 



The Zalambdodonta. 

 (Centetoidea Gill + Chrysochloroidea Gill.) 



The various families of Zalambdodonts, which are now so diverse in 

 structure, have been dispersed from their primal mode of life (which may 

 have been arboreal), into the same terrestrial, fossorial and semiaquatic 

 habits which have offered a seciu'e refuge to many other lowly vertebrate 

 groups. According to Matthew, who has discovered Chrysochloroids and 

 Centetoids in the Oligocene of North America {cf. pp. 258, 259) the mem- 

 bers of these groups have been driven southward from an original Holarctic 

 center of (listril)ution into such outlying faunal areas as Madagascar, West 

 Africa, South Africa, the West Indies and INIiocene Patagonia. 



THE CENTETID.E. 



The Centetidtie, once established in the great island of Madagascar, 

 deployed into a number of well marked lines of adaptation, which have been 

 described by Peters, Mivart (1867-68, 1871), Dobson (1883), Forsyth 

 Major (1897), Leche (1907) and others. Centetes parallels Didelphis and 

 the Creodonts in its enlarged canines, long skull, broad scapula, etc.; Eri- 

 culus parallels Erinaceus in several features of the dentition as well as in its 

 spiny covering; H emicenteies has evolved sectorial molars with long meta- 

 style blades; Oryzorycfes has acquired marked fossorial characters; Livi- 

 nogale resembles the aquatic shrews; finally, Potamogale represents an 

 otter-like adaptation to rapid swimming. Fortunately, as in the case of the 

 Marsupials, some of the more primitive members of this radiation have 

 survived to the present time, and from the various species of Microgale 

 Leche has been able to learn much of the morphological history of the group. 



Are the molars of the Cenietidw " pseudotritubercidar" '^ 



The molars of Centetes were formerly supposed to represent the tri- 

 tubercular dentition in a very simple form, but the researches of Mivart 

 (1867-68), Forsyth Major (1897), and M. F. Woodward (1896) have been 

 interpreted by Gidley (1906, p. 93) as indicating that the molars of Centetes 

 are, in fact, "pseudotritubercular," that their high pointed V represents the 



