GLIRES OF THE SANTA CRUZ BEDS. 415 



Of the skeleton, nothing is known but the tibia, fibula, pes, and parts of 

 the ulna and manus of S. d^^pl^catus. The manus (Plate LXVI, fig. 8) 

 is relatively larger than in Erethizon. The lunar, which is not coossified 

 with the scaphoid, is broad and very short proximo-distally, the radial 

 facet extending over nearly the whole dorsal face. The pyramidal is much 

 shorter than Erethizon, hardly more than a flat scale, thinning to an edge 

 on the ulnar side. A distinct central was present, as is shown by the 

 facets of the magnum, which is relatively much smaller than in Erethizon, 

 while the unciform is quite as in the latter; the same is true of the pisi- 

 form, which resembles that of the modern genus, but is relatively shorter 

 and more expanded at the free end. 



The metacarpals preserved are II, III, IV and V. It is not practicable 

 to determine whether the pollex was developed or rudimentary, for the 

 facet on metacarpal II is not decisive, though, judging from the analogy of 

 the pes, it seems probable that the pollex was functional. The other meta- 

 carpals are remarkably long and slender, especially II, III and IV. 

 Metacarpal II is rather longer than V, shorter than III or IV; the proxi- 

 mal end is oblique to the shaft in both directions, so as to give the bone 

 a somewhat twisted appearance ; the facet for the trapezoid is less concave 

 than in Erethizon and that for the magnum is somewhat smaller than in 

 t the latter ; on the radial side of the head is an articular surface for the 

 trapezium or for I. 



Metacarpal III is the longest of the series ; it differs from that of Ere- 

 thizon in having a well-defined process which overlaps the head of meta- 

 carpal IV and abuts against the unciform, while in the recent genus there 

 is no dorsal connection with the unciform. The shaft is slender and curved 

 forward ; the hemispherical distal trochlea is prominent, with a well-defined, 

 though shallow, supratrochlear fossa. 



Metacarpal IV is somewhat shorter and considerably stouter than III, 

 especially toward the distal end, where it becomes irregular. Metacarpal 

 V is much shorter than IV and relatively heavier. 



The phalanges are very similar to those of Erethizon, but not so long 

 in proportion to the metacarpus. The proximal phalanx is elongate, slender 

 and depressed, with slightly oblique proximal and distal facets ; the second 

 phalanx is also quite long and the ungual forms a long, curved and pointed 

 claw, cleft at the distal end. 



The tibia, which is separate from the fibula, as in Erethizon, is short 



