KELLOGG — NEW PINNIPED FROM UPPER PLIOCENE 
219 
between Trout Creek and Yerba Buena Creek, San Luis Obispo County, Cal- 
ifornia. The hill is probably the south one of the two 1,200 ft. knobs on the sheet. 
Horizon . — The specimens were discovered by Robert Anderson in March, 1909, 
in a formation of gravel and sand overlying typical Santa Margarita beds. These 
beds are considered to belong to the Paso Robles formation of the Upper 
Pliocene. 
The left humerus of this form differs very considerably from that of Alach- 
therium cretsii^ and also from that of Alachtherium antwerpie7isis^ and to a 
less extent from that of Trichecodoyi koninchii^ as figured by Van Beneden. 
Its most striking general characteristic is the antero-posterior compression of 
the distal end and the lateral compression of the shaft in the deltoid region. 
When seen in front (fig. la), the shaft appears considerably narrowed at the 
middle, arcuate in outline externally, and flaring out suddenly internally at the 
distal end. The external border no doubt arose below the overhanging posterior 
hook of the head of the humerus, as in Eumetopias juhata (fig. 2a), for its superior 
margin is so directed while it widens out distally as the supinator ridge. The 
deltoid ridge is prominently developed and forms the sharp anterior edge of the 
shaft. The anterior margin of the deltoid crest folds over the external border 
of ridge in both Eumetopias and Zalophus, while in Odohenus the folding over 
is on the internal side. In Mirowiga the deltoid ridge is low and the crest is 
uniformly rounded; this approximates more closely the type of deltoid ridge 
exhibited by this fossil humerus. However, the deltoid ridge itself curves or 
folds over the internal side to a slight degree in this fossil though not to such a 
marked extent as in Odohenus. 
When viewed from the internal side (fig. lb), the deltoid ridge is seen to curve 
prominently upward, though the antero-posterior diameter of the shaft in the 
deltoid region is not conspicuously wider than a lower trochlear portion, as is 
the condition in both Eumetopias juhata (fig. 2b) and Trichecodon koninckii 
(fig. 3b). This humerus resembles somewhat that of the common sea lion of the 
Pacific Coast, but is slightly smaller throughout than the humerus of the old male 
used for comparison, and a little broader at the distal end. The supinator crest 
is a little more flaring and sharp edged than in Eumetopias juhata, the trochlea 
is relatively wider, and the internal condyle is more produced. The external 
margin of the shaft is very thin and sharp edged in both Odohenus and this fossil. 
This margin is rounded in Eumetopias and Zalophus though in Arctocephalus 
australis it is slightly compressed and sharp edged. 
The coronoid fossa is apparently quite deep in comparison with those of 
Eumetopias juhata, Zalophus californicus, or Odohenus divergens, though the ex- 
posed surface of the humerus in this area has suffered slightly from erosion. 
This fossa is bordered internally by a broad rounded ridge extending up towards 
the lower end of the obliquely placed deltoid crest. This ridge is considerably 
reduced in Odohenus divergens and is more prominent in Zalophus californicus 
^ Van Beneden, P. J., Ann. Mus. Roy. Hist. Nat. Belgique, Atlas, vol. 1, pL 
3, figs. 1-2; pi. 4, fig. 1, Bruxelles, 1878. 
^ Ilasse, G., Bull. Soc. Beige de Geol., de Paleon., et dTIydroL, vol. 23, 
Memoires, pi. 5, figs. 1-4; pi. 6, fig. 1, Bruxelles, 1910. 
® Van Beneden, P. J., op. cit.. Atlas, pi. 7, figs. 1-2. 
JOUBNAL OF MAMMALOGY, VOL. 2 , NO. 4 
