10 



BULLETIN 110, UNITED STATES NATIONAL MUSEUM. 



Viewed from the side the structure of the skull of Antrodemus valens is light 

 and open. The posterior portion is deep dors'oventrally and moderately expanded 

 transversely. The facial portion is somewhat elongate, and tapers to the muzzel. 

 In all of the above respects this skull closely resembles that of Ceratosaurus nasi- 

 cornis, but when more closely compared they show many differences as will be 

 pointed out later. From the side view one special feature is the four large open- 

 ings on the side of the skull. These openings are all characteristic of the Thero- 

 podous dinosaurs, though in the several known genera they differ much in size, 

 shape and position. Another prominent feature is the high horn-like elevation 

 of the lachrymal bones extending well above the median dorsal surface of the skull. 

 The sharp upper surfaces of these elevations are rugose and furrowed with grooves, 

 which in life evidently were covered with chitinous skin. 



Pr.f. 



Fig. 3.— Skull and lower jaw of Antrodemus valens Leidt. No. 666, A.M.N. H. $ nat size, ang, angular; d., dentary; 

 ju, jugal; la, lachrymal; U.f, lateral temporal fenestra; mx, maxillary; na, nasal; n.a, anterior nares; o, orbit; 

 op.o, paraoccipital; P.mx, premaxillary; p.o, postorbital complex; pr.f, postfrontal; q.ju, quadeatojugal; sq, 

 squamosal; sur, surangular; 1, 2, 3, antorbital fenestrae. (After Osborn.) 



Viewed from above the skull is triangular in outline, wide behind and tapering 

 to a bluntly rounded nose as shown in plate 4, figure 1. The sides are sloping— 

 that is, from above downward — the bottom of the skull being wider than the 

 upper portion. 



Basioccipital (loc). — The basioccipital is composed of the convexly rounded 

 occipital condyle, and a long, narrow but heavy inferior process that joins 

 latterly with the descending branches of the exoccipitals or opisthotic elements. The 

 exoccipitals in this specimen contribute quite extensively to the formation of the 

 occipital condyle, see figure 4, although Osborn * has written, in describing the oc- 

 cipital region of Creosaurus (afterward regarded as Allosaurus, now Antrodemus) . 

 ' ' The basioccipital alone enters into the prominently convex condyle." The smooth 

 articulating surface continues well forward on the lateral and ventral surfaces of the 

 occipital condyle. This would appear to indicate a great mobility of the head in 



i Bull. Amer. Mus. Nat. Hist., vol. 19, 1903, p. 700. 



