XIV CONTENTS 



Figure Page 



370. Third and fourth upper premolars of Diplacodon elatus 440 



371. Upper molars of Diplacodon and Proiitanotherium compared 441 



372. Facial region of Eotitanoiherium osborni and Bronlotherium leidyi 441 



373. Map showing areas in which remains of titanotheres have been found 443 



374. Comparison of upper Eocene and lower OUgocene titanotheres 444 



375. Sections at base of horn in the six chief generic types of Oligocene titanotheres 445 



376. Position of the standard sections and contours of Oligocene titanotheres skulls 445 



377. Male and female skulls of Bronlotherium gigas 446 



378. Occipital view of skulls in different phyla of OHgocene titanotheres 447 



379. Influence of progressive brachycephaly on the auditory region of perissodactyls 447 



380. Inferior aspect of chin in Manleoceras • 449 



381. Upper molars of Menodus giganteus and Allops marshi 450 



382. Extreme dolichocephaUc and brachycephahc types of upper premolar-molar series in Oligocene titanotheres 450 



383. Third left lower molar of Bronlotherium leidyi 451 



384. Development of jaws and teeth, stage 4 452 



385. Development of jaws and teeth, stage 6 453 



386. Occiput of young skull of Brontops? brachycephalus 454 



387. Stages of wear in the adult upper grinding teeth of Ohgooene titanotheres 455 



388. Skull contours showing extreme divergence between Menodus giganteus and Bronlotherium platyceras 456 



389. Skulls of the menodontine group, side view 459 



390. Skulls of the bronototheriine group, side view 460 



391. Skulls of the menodontine group, top view 461 



392. Skulls of the brontotheriine group, top view 462 



393. Skulls of the menodontine and brontotheriine groups, palatal view 463 



394. Skulls of the menodontine and brontotheriine groups, front view 464 



395. Lower jaws of the Bronlotherium phylum 465 



396. Lower jaws of the Brontops and Menodus phyla 466 



397. Lower jaws of the Diplodonus and Allops phyla 466 



398. Heads of Oligocene titanotheres 466 



399. Sections at base of horn in five principal lower Ohgocene phyla of titanotheres 468 



400. Restorations of lower OUgocene titanotheres of the four principal genera 469 



401. Skulls of Rhadinorhinus and Bronlotherium, palatal view 470 



402. Skulls of Rhadinorhinus and Bronlotherium, side view 471 



403. Skulls of Rhadinorhinus and Bronlotherium, top view 472 



404. Lower jaws of Metarhinus fluvialilis and Bronlotherium halcheri 473 



405. Progressive evolution of the upper premolars in Bronlotherium. and its predecessors 474 



406. Progressive evolution of the upper premolars in Menodus and Brontops and their predecessors 474 



407. Progressive evolution of the lower premolars in Bronlotherium and its predecessors 475 



408. Progressive evolution of the lower premolars in Brontops and its predecessors 475 



409. Phyla of the Brontopinae and Menodontinae 477 



410. Evolution of the horns in the Brontops phylum 477 



411. Basal section of the horns in the Brontops phylum 477 



412. Progressive broadening of the nasals in the Brontops phylum 478 



413. Lower jaws of Teleodus primitivus, Brontops brachycephalus, and Allops walcotti? _ 478 



414. Sections and contours of skulls of Brontops brachycephalus 483 



415. Upper canines and incisors of Brontops brachycephalus 484 



416. Reconstruction of crushed skull of Brontops brachycephalus 485 



417. Left upper grinding teeth of Brontops brachycephalus 486 



418. Skull and horn region of Brontops brachycephalus? 486 



419. Sections and contours of skulls of Brontops brachycephalus and B. dispar 487 



420. Restoration of Brontops robuslus 492 



421. Sections and contours of skull of Brontops robuslus 493 



422. Skull of Brontops robuslus 495 



423. Lovi'er jaws of Brontops dispar and B. robuslus 496 



424. Sections and contours of skull of Brontops sp 497 



425. Hyoid bones of Brontops compared with those of the tapir, black rhinoceros, and horse 497 



426. Sections and contours of skulls of Diplodonus hicornutus and D. tyleri 498 



427. Sections and contours of skull of Diplodonus ampins 499 



428. Lower jaws of Diplodonus bicornutus and D. tyleri 503 



429. Sections and contours of skulls of Allops walcotti and A. marshi 610 



430. Upper teeth of Allops walcotti 511 



431. Skull of Allops marshi 513 



432. Lower jaws of Allops marshi and Allops? sp 514 



433. Sections and contours of skulls of Allops serotinus and A. crassicornis 516 



434. Coossified nasals and proximal part of horns of Allops? serotinus? 517 



435. Sections and contours of skulls of Menodus heloceras and M. trigonoceras 519 



436. Skull of Menodus heloceras 526 



437. Lower jaws of Menodus (Symhorodon) lorvus and M. trigonoceras 527 



