232 ■ . 



iiiaiufi of mastodons in that Stale. Specimens collected by him were sent to 

 Professor C U. Shrpurd, of Ainlierst, Massachusetts, who has submitted 

 them to the examination of the author. 



One of the specimens, a last inferior molar tooth, represented in Figs. 1, 2, 

 Plate XXI, was found together with the mutilated lower jaw and upper molars, 

 at Oak Springs, in Contra Costa County. The remains were obtained from 

 the rock at the' base of one of the rounded hills, of Tertiary age, mentioned 

 in Professor Whitney's Geological Survey of California, p. 32, stretching 

 along near the edge of the San Joaquin plain. According to Mr. William M. 

 Gabb, the formation belongs to the PHocene Tertiary period. 



A small photograph, sent to me by Dr. Yates, exhibits the lower jaw with- 

 out the ascending portions- behind, and with straight tusks projecting with an 

 upwar-d direction. The tusks appear to be as long as the jaw was in its com- 

 plete condition. 



The molar tootli has the same general form and constitution as the corre- 

 sponding one of the American mastodon, but is smaller than is usual in this 

 species. It resembles the plaster-cast above mentioned sufficiently to render 

 it pi'obable that it belonged to the same animal. 



The crown of the tooth is composed of four transverse pyramidal ridges, 

 each consisting of a pair of lobes, and conjoined in a common, broad, low 

 base, without a conspicuous offset- or heel. As in the cast of the Maryland 

 tooth, the inner lol^es are more mammillary or less angular than in M. ameri- 

 canus. In this respect they approach the condition, even more marked, how- 

 ever, in the M. angustidens of Eui'ope, and they are well separated to their 

 base as in M. americamis. The outer lobes of the crown have the same form 

 as in the latter, but are provided with distinct offsets projecting from their 

 inner part fore and aft. The contiguous- offsets come into contact, and thus 

 obstruct the transverse valleys of the crown. This arrangement accords 

 with that of the cast of the Maryland tootli. In M. ^wmcrtwws similar offsets 

 from the outer lobes are usually but feebly developed, and scarcely obstruct 

 the bottoms of the ti^ansverse valleys. 



The enamel worn from the summits of the anterior of the inner lobes 

 leaves a transverse ellipsoidal cup of exposed dentine, as usual in the same 

 position in the American mastodon. A greater degree of wearing on the 

 corresponding outer lobes has produced quadrilobate excavations of dentine, 

 in which the specimen agrees with the plaster-cast. In the same stage of 

 wear in M. ainericaniis, the excavations have a more lozenge-like outline. 



