FOSSIL MAMMALIA. 73 



all the conditions and appearances of those of a full grown animal ; and that they 

 present a marked difference of size as compared with those of the Mylodon 

 Harlani, as will be evident by the following admeasurements. 



ADMEASUREMENTS OF THE LOWER JAW OP MYLODON DARWINII. 



Inches. Lines. 



Length (as far as complete) .........17 6 



Extreme width, from the outside of one ramus to that of the other . . 9 



Depth of each ramus .......*.. 4 9 



Length of alveolar series .......... 4 8 



From first molar to broken end of symphysis ...... 6 



Breadth of symphysis .......... 3 7 



Longitudinal extent of symphysis ........ 4 6 



Circumference of narrowest part of each ramus ...... 5 9 



DESCRIPTION OF A CONSIDERABLE PART OF THE SKELETON OF A LARGE EDEN- 

 TATE MAMMAL, ALLIED TO THE MEGATHERIUM AND ORYCTEROPUS, AND FOR 

 WHICH IS PROPOSED THE NAME OF 



SCELIDOTHERIUM* LEPTOCEPHALUM. 



Of the large Edentate quadrupeds that once existed in the New World, sufficient 

 of the osseous remains of the gigantic Megatherium alone has been transmitted 

 to Europe to give a satisfactory idea of the general form and proportions of the 

 extinct animal. 



Different bones of the Megalonyx, Mylodon, and Glyptodon have been de- 

 scribed, but not sufficient of the remains of any individual of these subgenera 

 has, hitherto, reached Europe, or been so described as to enable us to form a 

 comparison between them and the Megatherium, or any of the existing Edentata, 

 in regard to the general construction and proportions of the entire skeleton. 



This state of our knowledge of the osteology of the singular giants of the 

 Edentate Order renders the remains of the present animal peculiarly interesting, 

 since, although the extremities are too imperfect to enable us to reconstruct the 

 entire skeleton, a sufficient proportion of it has been preserved in the natural 

 position to give a very satisfactory idea of its affinities to other Edentata, whose 

 osteology is more completely known. 



* SkeXis, femur ; diipwv, bettua ; in allusion to the disproportionate size of the thigh-bone. 



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