. 234 



The second specimen received from Professor Sliepard consists of the 

 fragment of a tusk, from Dry Creek, Stanislaus County, California. It was 

 discovered by Dr. Yates imbedded in the bluff of a hill, about ten feet above 

 the bed of the creek. The hill, upward of a hundred feet in height, is one 

 of those mentioned in Professor Whitney's Geological Sux-vey as being 

 scattered over the San Joaquin plain, at the base of the foot-hills of the 

 Sierra Nevada. 



The specimen is represented in Figs. 3, 4, Plate XXI, and is remarkable 

 from its exhibiting characters which indicate the species to have been nearly 

 related with the Mastodon augustidens of Europe. The molar tooth frdit 

 Contra Costa County, likewise presents a form which approximates it to the 

 same animal, so that it is probable both specimens may belong to the same 

 species. 



The fragment is six inches long, sliglitly curved in two directions, and in 

 transverse section (Fig. 3) is ovate, with the anterior pole acute. The pulp- 

 cavity, opening half the diameter of the tusk at its larger broken end, extends 

 half the length of the specimen. On one side of the tusk, as in Mastodon 

 augustidens, there is a broad layer of enamel, which extends from the acute 

 border two-thirds the width of the specimen. The enamel is somewhat 

 rugose, and is two-thirds of a line thick. In one position, near the smaller end 

 of tlie fragment, it has been worn through irregularly for the extent of about 1 J 

 inches. The convex or thicker border of the tusk has also been worn off to 

 an extent of two-fifths of the surface. The broken ends of the fragment exjiibit 

 the usual decussating lines of structure of the dentine so characteristic of 

 the ivory of the great proboscidians. 



The entire length of the tusk appears to have approximated two feet. The 

 other dimensions are as follows : 



Linos. 



Long diameter of the larger extremity 28 



Short diaTueter of the larger extremity 19 



Long diameter of the .smaller extremity 22 



Short diameter of the smaller extremity IG 



Breadth of enamel layer at larger extremity 22 



Breadth of enamel layer at smaller extremity 19 



In the form of the tusk and the possession of an enamel band it resembles 

 the same organ in the Mastodon augustidens. The specimen when first de- 

 scribed was viewed as probably representing a species distinct from that to 

 which the Contra Costa specimens pertained, and was therefore referred to an 



