510 



TITANOTHERES OF ANCIENT WYOMING, DAKOTA, AND NEBRASKA 



shape of the canine teeth it strongly resembles A. 

 marshi. 



At the same time Allops walcotti presents certain 

 resemblances to Menodus Tieloceras and was long re- 

 garded by the author as ancestral to Menodus, which 

 it foreshadows in its apparent dolichocephaly and in 

 the strongly developed external cingula of the pre- 

 molars as well as in the somewhat accelerated pre- 

 molar tetartocones. 



Description of the type sTcull. — The type skull, No. 

 4260, as figured on Plates CXI and CXII of this mono- 



The skull is in the seventh stage of growth. It 

 exhibits a slender but strongly indented occiput in 

 the center of which is a median ridge which projects 

 from the superior border. The cranial vertex is ex- 

 ceptionally long and narrow, with a decided lateral 

 crest overhanging the supratemporal fossa; in the mid- 

 region of this supratemporal crest we note (PI. CXI) 

 two lateral projections which are also observed both 

 in Allops serotinus (Nat. Mus. 4251) and in several 

 skulls of the Menodus phylum. In front of these are 

 the supraorbital projections. The horns are lateral 



B 



C 



D 



Figure 429. — Sections and contours of skulls of Allops walcotti and A. marshi 



A, Allops walcotti, Nat. Mus. 4260 (type); lower levels of Chadron A; a very primitive stage, approaching both Brontops hrachycephalus and Menodus Jieloceras in the 

 character of its sections. Low horns elongate in basal section and placed not far in front of the orbits, nasals long and narrow, zygomata slender. No very definite 

 marks of affinity with Allops are revealed by the sections. B, A. marshi, Am. Mus. 501 (type) ; horns elongate trihedral in basal section and placed considerably in 

 front of the orbits, nasals broad distally, zygomata little expanded. C. A.marslii, Am. Mus. 1145 (paratype); the sections differ little from those of the type, although" 

 the skull as a whole is broader. D, A. marshi. Harvard Mus.; differs somewhat from the type in the steeper profile of the horns, basal section obliquely trihedrali 

 zygomata little expanded, parietal vertex narrow. One-eighth natural size. 



graph, was referred mistakenly by Marsh to Bronto- 

 therium gigas notwithstanding its marked inferiority 

 in size to the type of that species, which properly 

 belongs to the Brontotherium phylum. In studying 

 the plate and figures emphasis must be laid on the 

 fact that the skull is extremely crushed laterally, 

 and that its original mesaticephalic proportions are 

 artificially increased into dolichocephaly. In other 

 respects the plate as well as the accompanying figures 

 and sections give an admirable idea of the formation 

 and proportions of this primitive titanothere. 



in position, overhanging the sides of the face and 

 of an elongate-oval basal section anteroposteriorly, 

 distinct from that of the type of Allops marshi. The 

 long axis of the section is anteroposterior, whereas 

 in A. marshi it is oblique; the horn rises only 70 

 millimeters above the side of the narial aperture, 

 40 millimeters above the vertex of the skull. The 

 nasals also resemble those in the type of A. marshi; 

 they extend very far forward, contracting slightly, 

 and cleft at the tips. The relative elongation of the 

 face is a decided feature (PL CXI, A'), the bridge over 



