48 



BULLETIN 110, UNITED STATES NATIONAL MUSEUM. 



CHEVRONS. 



With specimen No. 8367, U.S.N.M., 

 there are six chevron bones preserved. 

 Judging largely from their relative posi- 

 tions as found in the quarry (fig. 21) they 

 appear to represent the first, second, third, 

 fourth, fifth, and seventh of the [series. 



The anterior chevrons of Anirodemus 

 valens can be at once distinguished from 

 those of Ceratosaurus nasicornis, by 

 their greatly expanded articular proxi- 

 mal ends, the wider, antero-posteriorly, 

 and more backwardly curved shaft, and 

 their relatively shorter lengths. 



One of the most striking peculiarities 

 of the Anirodemus chevrons is the devel- 

 opment on the anterior side of the prox- 

 imal end of two projecting spurs, which 

 extend forward on either side of the 

 haemal opening, as shown in figure 32. 

 The two branches of the chevrons are 

 joined together by a bridge of bone 

 above the haemal canal. In this respect 

 they differ from Gorgosaurus with its 

 two articular ends distinct from one 

 another. The width of the articular 

 end increases posteriorly. The longest 

 chevron, probably the fourth, has a 

 greatest length of 252 mm. with a great- 

 est transverse width at the proximal end 

 of 79 mm. 



The lack of a distinct beveled facet 

 on the lower posterior border of the 

 first caudal would appear to indicate 

 that the series of chevrons in Antrode- 

 mus begins between the first and second 

 caudal vertebrae, as in Ceratosaurus 

 where it was found in position. 



Cervical ribs. — In specimen No. 4734, 

 U.S.N.M., there are present on the right 

 side, the ribs belonging to the third, 

 fourth, fifth, sixth, eighth, and ninth cer- 

 vical vertebrae. Apparently, it is the first specimen found having a considerable num- 

 ber of the ribs preserved, and they show those restored on the mounted skeleton of 



Fig. 31.— Series of five caudals from near the distal end 

 of tail of antrodemus valens leidy. no. 4734, u.s.n.m. 

 \ nat. size. Drawn from the right side as found in the 



MATRIX. 



