1899.] 



TLEXODONT MOLAHS OE MAMMALS. 



.559 



with again iu many Insectivora {Talpa, Tupaidae, Soricidse, &c.), 

 and likewise in the Chiroptera, especially in Vespertilionidse, the 

 most numerous and ancient family. In all these groups the 

 molars differ from those of Proteoclideljiliys only by the greater or 

 lesser development of cusp ma, by the suppression o£ cusp ai or 

 its fusion with ae, and by the varying degree of simplification of 

 the posterior lobe. 



Fig. 3. 



->>-i^ 



y- a 



Cyonasiia argcntina: fifth right lower molar, superior ('<) and external (/)) 

 aspect, nat. size. — Eocene ; Patagonia. 



Another branch, likewise originating from the most primitive 

 Microbiotheridfe, are the diprotodont Marsupials, which comprise 

 the extinct Multituberculata of the Northern Hemisphere and 

 Argentina, the numerous Paucituberculata of South America, and 

 the Diprotodonts of Australia (Hypsiprymnoidea). Their most 

 primitive type is that of the Grarzonidse. The lower molars of 

 Garzonia or HalmaHplms (fig. 4) are not distinguished by any 



Halmariphus didclpholdes : fifth right lower molar, superior (a) and external {h) 

 aspect, eight times uat. size. — Eocene ; ratagouia. 



essential character from those ol^ the Didelphyida3 ; their teeth 

 exhibit the six cusps of those of Proteodideljjhys. with an almost 

 similar disposition and with the same external cingulum, c. Some 

 species depart slightly from this form by the internal displacement 

 of the two median cusps, the anterior and the posterior, so that 

 each molar presents on the internal margin a range of four cusps, 

 as can be seen in the molars of a Cretaceous species of HahnarijjJius, 

 or a nearly related genus (fig. 5). In tlie Epanorthidse the paired 

 cusps ae, ai, and jjfi, pz, are conueeted, forming two semicircular 

 crests. In the Abderitidae the same cusjjs constitute two feebl)^ 

 accentuated, transverse crests. The slightly more recent Diproto- 

 donts of the Parana deposits {Zygolestcs) exhibit the same crests 

 more accentuated ; they are still more developed in the exisrinp; 

 South-American genus C'cenolest's of O. Thomas, the molars of 

 which have assumed the same form as those of the Australian 



