( to ) 



absence of the crista occipitalis and the tendency of the crista 

 lambdoidea to develop on the skull into ;i sagittal ridge 1 ). 



What reasons had v. Beneden to coordinate the cranial fragment to 



the mandible on which Alachtherium is based? He does not slate 

 them anywhere: 



"On ne possédait d'abord de ce curieux Amphitétïen d'autre os 

 que le maxillaire .... Nous rapportons a ce nième animal . . . ., 

 le crane que nous réprésentons . . . ., les vertèbres cervicales de. 

 etc La forme du maxillaire inférieur indique nne confor- 

 mation toute particuliere de tons les os en face . . . ." 



The question now is whether on the contrary it cannot be shown 

 that cranial fragment and mandible do not belong- to each other. 

 This seems indeed to be the case : 



The lower jaw deviates strongly from that of Tricheclms and 

 points in fact to a "conformation toute particuliere de tons les os 

 en face". But as the hind skull of Alachtherium does entirety 

 conform to t lie Trichechus type, it is unjustifiable to assume for the 

 lacking part an entirely deviating shape, only in order to be able 

 to tit the skull to the lower jaw. 



The hind skull has much more massive and coarse bones than 

 Trichechus, the mandible on the other hand is larger than that of 

 the walrus, but of a much more elegant and fine build: also in 

 their structure skull and lower jaw have consequently opposite 

 characters. Also the lower jaw is too big for the cranial fragment. 

 For the cranium belongs to an old animal and so the lower jaw 

 should certainly not be much too big for the skull. If we now 

 divide two dimensions of the walrus and of Alachtherium, we find : 



Walrus Alachtherium Alacht. : Walrus 

 distance of the fossae glenoid eae 13.5 14.5 107 



length of the mandible 24.7 35.7 144 



Hence we here obtain again such abnormally great differences of 

 two dimensions between the walrus and Alachtherium that the 

 otherwise considerable analogy of the skulls does not permit us to 

 ascribe mandible and skull to one species. The principal argument, 

 however, is found in the shape of cranium and mandible. 



We saw that with Alachtherium the fossa glenoidea has a much 

 less free situation than with Trichechus. With the latter the mandible 

 has a short, vertical coronoid process, which consequently easily 

 finds a place in front of the squamosum. The lower jaw of Alach- 



•) J. A. Allen (30) slates about Trichechus obesus that this also has a small 

 bulla ossea. 



