Page 14 - maxson1928

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1·,lERYCHIPPUS CALIFORNICUS Merriam

The tooth upon which the recognition of this species is based is

a superior' right molar two or three showing a slight amount of wear
(No. 18, Calif, Inst. Coll,i. Its height is almost twice as great as its

antero-posterior diameter. The coating of cement is rather light. Curvature

of the crown is moderate. 'l'he transverse diameter diminishes very

pronouncedly toward the grinding surface. In size it is comparable to

1
111, califoruicus from the r1 emblor of the north Coalinga district and is
slightly smaller than M. sumani from the Mohave Desert Barstow. ?late I.

Figure 1. illustrates its proportions.

The protocone occupies an almost median p~sition on the inner side

of the grinding surface. It is a flattened oval in cross-section and

judging from both form and position along the inside of the crown it is

separated from the protoconule up to an advanced stage of wear. Plication

of the fossettes is moderate and approximates that in both M. californicus

and hl. isonesus. However, the post-fossette is open posteriorly to the

base of the crown. The interior wall of the post-fossette forms the

exterior wall of the hypocone. A similar condition is sometimes found in
2
M- of M. sumani and in other merychippine forms. A small anteriorly

directed pli cahallin is present.

Measurements of J:~o .. 18
l'
Antero-posterior diameter (10 mm. above base) ------- 18.l mm.

l'ransverse II " " ------- 15.0

Antero-posterior diameter lat base of crown) ------- 18.2

Transverse fl 11 It " !I ----·-- 18.7