GEOLOGICAL Sf< '< 'KSSK i.\ OK MOI.Ai; TYl'KS 



93 



cusps, or the crown is more or less basin-shaped, with an irregular, 

 raised border (D. br achy tiara) \ the latter teeth are analogous to thn-r 

 of .!//>/ Wr.sYf.s, of the Upper Triassic or Ehsetic of (iermany (Fig. 48).* 

 It will Vie observed that the opposite series of grinders converge towards 

 each other anteriorly ; these teeth are therefore multicuspidate but not, 

 strictly " multituberculate," because in the true Multituberculates the 

 opposite tooth rows are parallel and the jaw motion palinal or from in 

 front backward. These teeth, with irregularly disposed tubercles or 

 basin-shaped crowns, are most closely analogous to those of certain 

 squirrels. 



The fourth type is the multituberculate, seen in the genus Tritylodon^ 

 (Figs. 46, 48), iu which the opposite series of teeth arc parallel: tin- 



ftlHX 



Kn;. 4'i. Ti-il"iijilni>. 



>,-,ix. anterior portion of the skull iiy,un the left face, two thirds natural 

 size. After Owen. 



grinding teeth are covered with tubercles arranged in regular, parallel 

 rows, with grooves between, adapted to a fore-and-aft motion of the 

 jaw. 



Certain of these TheriodontsJ present the same dental formula as in the 

 generalized dentition of the most primitive mammals. Their resemblances 

 to the Protodonta and Multituberculata in tooth structure are so striking 

 that since they belong practically to the same geological period the 

 probability of actual affinity is to be considered. 



*[But these are upper not lower teeth; they are elongate transversely (as in upper 

 molars generally) not antero-posteriorly as in the lower molars of M' -r<>l, xte*. The lower 

 molars (Fig. 45, Nos. 4, 5) were single-rooted, round teeth, with a depressed crown bearing 

 a low transverse median ridge (Broom). ED.] 



t [Broom has recently shown that Tritylodon is more probably a mammal. Kr>.] 



J [Certain Theriodonts (e.g. Trinu-ltodon) had more or less lophodont molars with a 

 low, irregular medium cross crest. Traces of such a crest are seen also in Ornithorynchus (1) 

 Kurfodoit, Diplocynodon, Dryolextex, Sriiirn*, Lcpu*. Similarly in the lower molars a 

 transverse crest connecting the protoconid and metaconid is seen in Diademodon, Trim- 

 clwiloii, Paurodon, Amblotherium, C<nt</>*, etc. This cross crest may possibly liave some 

 bearing on the origin of the tritubercular type. ED.] 



