426 



University of California Publications. 



[Geology 



ridge between, instead of close together. Ridge on anterior face 

 small. Entoeonid ridge rounded rather than square. The in- 

 cisors and P 4 are large in proportion to other teeth. 



General Description. — P 3 is a round, single-rooted tooth, com- 

 paratively smaller than P 4 and consisting of one high cone on 

 the outer, posterior side, around which circle two small ridges. 

 P 4 consists of one low anterior and two posterior ridges, set trans- 

 versely to the median line of the jaw, and with a rounded 

 tubercle on the inner side between the two ridges, from the base 

 <if which a smaller ridge runs to the posterior edge of the third 

 transverse ridge; M 2 has three transverse ridges, the middle one 

 slightly higher than the other two and running up into a tubercle 

 on the outer edge of the tooth and an inner tubercle which seems 

 to he a continuation, toward the back of the tooth, of the central 

 ridge. M 3 consists of two transverse ridges, the second running 

 up into a tubercle with an inner tubercle extending from it, and 

 a low. rounded heel with several flattened ridges. P 4 has a 

 protoconid and metaconid, the latter somewhat higher and con- 

 nected with the protoconid by a ridge, and directly between them 

 anteriorly and set low on the tooth, a curved ridge, almost the 

 equivalent of a tubercle, behind which is a small pit. The hypo- 

 eonid is connected with the protoconid by a ridge and the ridge 

 of the entoeonid curves around to the base of the metaconid, the 

 whole heel being slightly lower than the protoconid. M 1; M 2 , and 

 M 3 have a high metaconid with a small accessory ridge merging 

 into that of the entoeonid, and a low protoconid and hypoconid 

 with a fossette between. 



A comparison of A. minor with specimen no. 3079 of the 

 California Museum of Vertebrate Zoology, which is a left ramus 

 of the lower jaw with incisor and P 4 , found at the head of Big 

 Creek, Humboldt County, Nevada, and referred tentatively to 

 A. flaviventer, shows the following specific differences. In no. 

 3079 the protoconid and metaconid are much higher, the latter 

 is more swollen, and there is no ridge between them, the two 

 edges meeting at a sharp angle ; the protoconid and hypoconid 

 are closer together; the anterior ridge is longer and more bulg- 

 ing ; and the entoeonid ridge is square, rather than rounded. 



