. Bulletin of the Museum of Comparative Zoology at Harvard College. Zoology. WOOD AND PATTERSON : OLIGOCENE RODENTS OF PATAGONIA 368 protocone-anteroloph crest curves forward and outward, losing altitude progressively, so that the extremity is far below the level of the apex of the paracone. The paraflexus deepens lingually, and would eonvei-t to a long, narrow parafossette. Frotoloph and mure form a curving crest connecting the pai-acone and liypocone. Opposite the protocone, there is a short blunt projec- tion that, with wear, would unite the two crests at this point. The paracone is joined
. Bulletin of the Museum of Comparative Zoology at Harvard College. Zoology. WOOD AND PATTERSON : OLIGOCENE RODENTS OF PATAGONIA 368 protocone-anteroloph crest curves forward and outward, losing altitude progressively, so that the extremity is far below the level of the apex of the paracone. The paraflexus deepens lingually, and would eonvei-t to a long, narrow parafossette. Frotoloph and mure form a curving crest connecting the pai-acone and liypocone. Opposite the protocone, there is a short blunt projec- tion that, with wear, would unite the two crests at this point. The paracone is joined to the external part of the posteroloph by a gently curving crest that bears two minute cuspular elevations. Frotoloph, mure, posteroloph and this external crest isolate a large, deep fossette. From the external crest, opposite the second cuspular elevation, a prominent spur projects into this 24. fDasyproetidae, gen. ct sp. indet. Left upper cheek tooth, T A T O 1 1 9 ,. « Fig M. , no. A 52-113, x 6 A slight swelling is present on the outer surface of the mure. The region of the hypocone is the highest part of the unworn crown. No trace of- cement is present. We are in some doubt as to whether this tooth should be in- terpreted as P* or as a molar. It agrees in outline with P^ of Santacruziau SeJe)-omys as figured by Scott, but not with Fields' (1957) referred material. It differs from both in the presence of the large spur in the posterior valley. This structure appears to be a remnant of a metaloph, the swelling on the mure repre- .senting the aliorted inner end of the crest. So molariform a premolar would be decidedly exceptional in the Deseadan. If the spur and swelling be regarded as a metaloph in process of formation, then such a mode of origin would be exceptional for P* among caviomorphs. Agreement with the upper molars of Santacruziau Scleromys is close. These teeth lack the metaloph entirely, and, since this is clearly a secondary condition, the. Pleas
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