NO. 1554. A NEW HORNED RODENT— GIDLEY. 631 



The clavicles (Plate LXIV, tig. g) are very large, with heavy 

 expanded ends for the cartilaginous attachments of the scapula and 

 steriuim. 



There are three elements of the sternum preserved in the type 

 (Plate LXIV, fig./), including the presternum. This element is"a 

 comparatively large, irregularly shaped bone, with the transverse 

 diameter somewhat exceeding the antero-posterior. Its ventral face 

 is not keeled, and its thick anterior border presents a wide, shallow 

 notch between the clavicles. In form and general proportions the 

 presternum is curiously like the presternum or manul>rium in the 

 human skeleton. The remaining two elements, sections of the meso- 

 sternum, are very much smaller than the presternum, and are short 

 and thick. 



The bones of the fore limbs and feet are short and massive through- 

 out, and are greatly modified. The scapula (Plate LXIII, fig. a, and 

 Plate LXIV, fig. a) is large and Aplodontia-like in form. The spine 

 is high, tbin-edged, and bears a moderately well-developed mata- 

 cromion. In Castor the spine is thick-edged and slopes rapidly from 

 the acromion in a nearly straight line to the upper scapular border. 

 The acromion is broken away in the type specimen. The glenoid 

 cavity is shallow and continuous, with the anterior face of the heavy 

 downwardly curved coracoid process. 



The humerus, Plate LXI, fig. c, is short and massive, with its processes 

 and ridges well developed for strong musclature. The great tuber- 

 osity extends well above the head of the humerus. The deltoid ridge 

 is low but extends far down the humerus, ending in a strong spur-like 

 process well below the middle point of the shaft. In Vendoganlxis 

 this process is situated just below the middle of the shaft. In A])lo- 

 dontla it is a little a])ove that point. The supinator ridge is thin and 

 very broadl}' expanded. This, together with the unusually well-devel- 

 oped condyles, gives a great breadth to the distal end of the humerus, 

 which equals nearly one-half its entire length. There is present a 

 large entepicondj^lar foramen, as in the Aplodontidjc and Sciuridw. 



The forearm, as compared with most other rodents, is unusually 

 short, the shafts of the radius and ulna being only two-thirds the 

 length of the humerus. The total length of the idna, however, some- 

 what exceeds that of the humerus, owing to the great development of 

 the olecranon. The shaft of the radius i« small and round proximally, 

 but is much expanded laterally at the distal end. The distal end of 

 the ulna extends considerably below the end of the radius, as shown 

 in Plate LXII, fig. a. 



The only elements of the carpus preserved in the present specimen 

 are the scapho-lunar and unciform. These are broad and thin, indi- 

 cating a broad, short carpus. The metacarpus and proximal digits 

 indicate also a very short and broad fore foot. The stout, heavy 



