EDENTATA OF THE SANTA CRUZ BEDS. 



169 



Cholcepiis ; all but two or three, at most, of the ribs have prominent 

 tubercles. The sternal ribs are fully ossified and articulate with the 

 sternum by means of well-formed heads and tubercles. 



(7) The sternum is of similar type in both Megalonychidce and Planop- 

 sidce, and as this type is essentially that of My/odon, it may be inferred that 

 the Santa Cruz Mylodontidce had a sternum of the same character. The 

 manubrium, which varies in form, is a depressed plate and may have an 

 .emarginate anterior border, or have a heavy, tongue- 

 like projection from that border ; it is provided with 



short processes for the clavicles. To the segments of 

 the mesosternum, the number of which is not known, 

 Owen's description of the same parts in Mylodon will 

 exactly apply. " The bones forming the body of the 

 sternum may be divided into two parts, a broad and 

 flat posterior [dorsal] plate of quadrate form and an 

 anterior [ventral] rhomb or cube projecting from the 

 middle of the plate, and they each present not fewer 

 than ten articular surfaces, two for the contiguous 

 sternal bones and the remaining eight for portions of 

 two sternal ribs " ('42, 54). 



(8) Several well-preserved scapulae have been collected, but most of 

 them were found isolated and cannot be definitely referred to their genera 

 and species. However, they are of very uniform type, varying only in 

 outline and not very strikingly even in that respect. In form, the scapula 

 resembles that of Cholcepus rather than that of any of the Pleistocene 

 genera ; for most of its length the spine is comparatively low and is so 

 placed as to make the prescapular fossa much larger than the postscapu- 

 lar ; the acromion is very long and is united with a process of the cora- 

 coid, but this bony bridge or loop does not extend nearly so far below the 

 level of the glenoid cavity as it does in Cholczpus. The coracoid is very 

 large, considerably broader in proportion than that of Chol&pus, which 

 makes the coraco-scapular foramen smaller ; it is connected with the 

 scapula by a suture which persists till a late period, but eventually disap- 

 pears. The glenoid cavity is relatively small and shallow. 



(9) The clavicle, which has been found in connection with only a few 

 species, is rather short and slender, subcylindrical in shape and with a 

 slight sigmoid curvature. 



FIG. 20. 



? Hapalops sp. Right 

 scapula, x \. 



