Mylodon harlani, from Rock Creek, Texas. 375 



in proportion to their length and do not give, at any rate in 

 their present condition, so great an impression of power. 



Dimensions. 





Cast 



10264 



10266 



Length over all 



Girth of shaft at mid-length 



Proximal end, transverse diameter 



ant. -post, diameter 



Distal end, transverse diameter. 



ant.-post. diameter 



mm 



264 



226 



99* 



101* 

 49 

 90 



mm 



233 



216 



170 



111-5* 



141 



96-5 



49 



87 



mm 



222 



202 



166 



111-5 



133 



103 



Shaft, least ant.-post. diameter 



least transverse diameter 



46 

 79 



* Somewhat reduced through abrasion. 



Foot. — Astragalus, (see fig. 13 a, h.) — There were three 

 astragali collected from the Texas quarry and unfortunately 

 all were from the right limb. One, the most perfect, articu- 

 lates very well with tibia No. 10266, a second not so well w T ith 

 No. 10264, while the third, the least complete, has been 

 assigned the number 10265. These astragali differ materially 

 in certain proportions, notably 10266, which has much the 

 stoutest ascending process, though in certain other dimensions 

 it is the smallest of the three. This bone shows a remarkable 

 difference in the character of the navicular articulation, which 

 is deeply concave, the concavity covering the entire facet. In 

 No. 10264 this area is almost a plane, with a very small 

 depression in the center which seems to be largely the result 

 of fracture, while in the third astragalus this surface has un- 

 fortunately been destroyed. Of two naviculars which are pre- 

 served, one has a rounded protuberance corresponding to the 

 depression in No. 10266, while the other shows a flat surface, 

 although otherwise the two bones compare curve for curve. 

 A cast from the Perkins series is that of a left astragalus, and 

 while this portion of the bone was somewhat injured, there is 

 no appreciable depression indicated, though a slight one may 

 have been present. 



Owen says (p. 117) : " The astragalus is of an irregular pyra- 

 midal form, the posterior end forming the apex, and the base, 

 which is turned forwards, being rudely divided into three 

 large tuberosities. If the foot be placed with the sole flat on 

 the ground . . . the astragalus, naturally coadapted to the 

 other tarsal bones, has its fibular or outer side uppermost, and 



Am. Jour. Scl— Fourth Series, Vol. XXXIX, No. 232.— April, 1915. 

 25 



