86 Field Museum of Natural History — Geology, Vol. VI 



The structure called the anterior ridge by Van Kampen is unques- 

 tionably the crista meati. As in T. cristatum it is indistinguishably 

 fused with the post-glenoid process of the squamosal, the fissura 

 glaseri being confined to the anterior half of the squamoso-tympanic 

 contact. As a result of this fusion Van Kampen was in some doubt 



fov -t-fl m. 



Fig. 8. Psewdo^J/potfeeriMTO pseudopacfej/ffnat/iMTO (Ameghino) . Cranial region of left side. Lateral 

 and a little obliquely ventral view. A.M. No. 14509. x 2/3. cr.m., crista meati; j.ov. + f.l.m., fora- 

 men ovale and foramen lacerum medium; p.o.e., porus acusticus externus; p.ffJ./., post-glenoid foramen; 

 p.gl.pr., post-glenoid process; iyhl., tympanohyal; v.pr.hy., vagina processus hyoidei. 



as to whether this crest was from the meatus or whether it was a 

 continuation of the post-glenoid process. From comparisons with 

 other notoungulates it is at once apparent that it is from the meatus. 

 The crista meati in P. pseudopachygnathum bears a prominent, 

 ventrally directed process or spine on its infero-external angle, 

 precisely as in toxodonts (sensu strictu). Van Kampen describes 

 two of these spines on the crest of T. cristatum. This author con- 

 sidered that Typotherium might have possessed a meatus spurius, 

 but this is certainly not the case. 



The vagina processus hyoidei is rather large and deep, and is 

 situated at the posterior end of the bulla halfway down its lateral 

 side. Mesially, anteriorly and laterally it is bounded by the 

 tympanic, posteriorly the post-tympanic process of the squamosal 

 appears to form part of the wall. As in most typotheres, the paroc- 

 cipital process does not enter into the boundary of the vagina; this 

 is not a condition prevailing throughout the suborder, however, for 

 in some genera, e.g. Cochilius, the paroccipital process forms a 

 part of the posterior wall. A portion of the tympanohyal is still 



