1921] Prick: Faunas of Bautista Creek and San Timoteo Canon 407 



Description. — Portion of skull and posterior maxillaries of the 

 type specimen: The fourth crest of the right molar (fig. 160) has 

 but slightly protruded beyond the alveolus; the heels of both molars 

 and the last lobe of the left molar are still buried beneath the ptery- 

 goid. A cross-section of the jaw, however, illustrates the very small 

 amount of heel occurring in this form. The skull portion shows the 

 foramen magnum, the vomer, and the edges of the great alveolar 

 pouch limited posteriorly by the overarching process of the pterygoid. 



The third molar in the right maxillary (no. 23501, fig. 160) is 

 furnished with four main, deeply notched, outwardly diverging, 

 transverse crests; and, as seen in cross-section of the opposite jaw, a 

 rudimentary heel. The anteroposterior diameter of the specimen is 

 slightly less than twice its transverse width, being widest at the second 

 main crest and narrowest at the heel. The two forward crests have 

 come into function, being abraded and polished ; the posterior crests 

 are still rugose. Each m.ain crest consists of a large outer and larger 

 inner pyramidal lobe, connected medially by three small subsidiary 

 conules. Two of these are thrown off from the inner base of the outer 

 lobe, and one from the inner base of the inner. Two additional conules 

 rise laterally from the anterior and posterior faces of the inner lobes. 

 They lie in a triangle with the tip of the main lobe and, abutting for- 

 ward and aft against the corresponding conules of the next adjacent 

 crests, form a low, anteroposteriorly directed ridge which obstructs 

 the transverse valleys. In the worn stage this trianguhir grouping 

 of the inner cusps and accessory conules gives rise to the trilobed 

 pattern of the inner half of the upper teeth. 



A second upper molar from the left side (no. 23503, fig. 16-1) is 

 three lobed, and the two anterior crests are somewhat worn, especially 

 toward the inner tooth margin. Two dentine tracts are exposed in 

 each transverse crest, an outer tract of oval form appressed against 

 an inner trilobed area. The lateral margins of the triangular area of 

 adjacent crests abut against one another. A small jiyramidal shelf 

 at the posterior tooth extremity connects with the triturating surface 

 by upwardly and inwardly directed ridges. 



Figs. 160 to 165. Trilophodon shepardi edensifi, n. subsp. Dentition. All 

 figures X %. Fig. 160, posterior portion of jaw of type with teeth, no. 23501, 

 opclusal view (heel of right molar shown by dissection), and lateral view (posi- 

 tion of heel shown by dotted line, portion of maxillary omitted); fig. 161, worn 

 molar showing two lophs, no. 2.3505, occlusal view; fig. 162, upper molar, no. 

 23504, associated with jaw specimen, no. 23501, occlusal view; fig. 163, premolar, 

 no. 23506, occlusal view; fig. 164, u))per molar, no. 23503, associated with jaw 

 specimen, no. 23503, occlusal view; fig. 165, lower molar, no. 23502, occlusal and 

 lateral views. Eden beds, California. 



