426 



V niversity of California Puhlicatio)is i)i Geologij [Vol. 12 



for a inountt'd individual, in pursuance of a plan to monograph the 

 ground sloth group from Rancho La Brea, was most generously granted 

 by the late director of the Museum, Dr. Frank S. Daggett. The task 

 of assembling the skeleton and preparing the mount has been admir- 

 ably accomplished by ]\Ir. J. W. Lytic, preparator at the Museum. • 

 The photograph was taken by Mr. L. E. Wyman, and permission to 

 reproduce it has been kindly given by Mr. Howard Robertson, Acting 

 Director. 



CHARACTERS OF MYLODON HARLANI 

 Dermal ossicles present in skin. 



BkulP with iDremaxillaries usually loosely joined, sometimes co- 

 ossified, with maxillaries. 



^ . . .5-4, 5-4 

 Dentition^ ^— 



Thyroid cartilage sometimes ossified. 



Vertebral formula: C 7; T 16-15; lumbar-sacral 8-9; Ca 21. 



Chevron bones articulate with caudal vertebrae. Anterior chevron 

 consists of a right and a left piece which are not joined in median line. 

 In middle portion of tail chevron bones are Y-shaped with haemal 

 spines broadened anteroposteriorly. 



Separate cervical rib sometimes present, articulating with seventh 

 cervical vertebra. Fifteen j^airs of body ribs in mounted specimen. 



Seven sternal elements. Sternal ribs ossified. 



Clavicle present. 



Anterior limb heavy ; scapula with coraco-scapular foramen and 

 with complete coraco-acromial arch ; humerus with no entepicondylar 

 foramen. Manus similar to that of Mylodon robKstus. Digits 4 and 

 5 greatly reduced. 



Pelvis with greatly expanded ilia ; pubic symphysis short. 



Posterior limb massive ; femur broad, very heavy, and lacking a 



third trochanter. Foreleg shortened. Length of tibia (T) — _ 



Length of femur (F = 1) 

 Pes- as in Mylodon robustus; weight of body supported by large calca- 

 neum and outer side of metatarsal 5. 



1 Stock, C, Skull and dentition of the mylodont sloths of Eaneho La Brea, 

 Tniv. Calif. Publ. Bull. Dept. GeoL, vol. 8, pp. 319-334, 1914; Further obser- 

 vations on the skull structure of mylodont sloths from Eaneho La Brea, Univ. 

 Calif. Publ. Bull. Dept. Geol., vol. 10, pp. 165-178, 1917. 



2 Stock, C, Structure of the pes in Mylodon harlani, Univ. Calif. Publ. Bull. 

 Dept. GeoL, vol. 10, pp. 267-286, 1917. 



