MABSH.] 



CIPLODOCID.E. 



175 



through the centra, a thin septum usually remaining. In the median 

 caudals a deep cavity on each side exists, as shown in figs. 24-26, below. 



On the distal caudals the lateral cavity has nearly or quite disap- 

 peared. All the caudal vertebrse are proportionally shorter than in 

 Diplodocus, and their chevrons have no anterior projection, as in that 

 genus. 



The remains on which the present description is based are from the 

 Atlantosaurus beds of South Dakota, about 200 miles farther north 

 than this well-marked horizon has hitherto been recognized. 1 



Fig. 24. — Candal vertebra of Barosaurus lentus Marsh ; side view. 

 Fig. 25. — The same vertebra, in section j front view. 

 Fir,. 26. — The same vertebra; bottom view. 

 All the figures are one-eighth natural size. a. anterior end; c, face for chevron; /, lateral cavity; 

 p. posterior end; *. section. 



DIPLODOCIDJE. 



DIPLODOCUS. 2 

 THE SKULL. 



The skull of Diplodocus is of moderate size. The posterior region is 

 elevated and narrow. The facial portion is elongate and the anterior 

 part expanded transversely. The nasal opening is at the apex of the 

 cranium, which from this point slopes backward to the occiput. In 

 front of this aperture the elongated face slopes gradually downward to 

 the end of the muzzle, as represented in PI. XXV, fig. 1. 



Seen from the side the skull of Diplodocus shows five openings: a 

 small oval aperture in front, a large antorbital vacuity, the nasal aper- 

 ture, the orbit, and the lower temporal opening. The first of these has 

 not been seen in any other Sauropoda ; the large antorbital vacuity is 

 characteristic of the Theropoda also; while the other three openings 

 are present in all the known Dinosauria. 



On the median line, directly over the cerebral cavity of the brain, 

 the type specimen of Diplodocus has also a fontanelle in the parietals. 

 This, however, may be merely an individual peculiarity. 



The plane of the occiput is of moderate size, and forms an obtuse 

 angle with the frontoparietal surface. 



The occipital condyle is hemispherical in form, and seen from behind 

 is slightly subtrilobate in outline. It is placed nearly at right angles 



1 Strata that may represent this horizon have been observed still farther north, especially in Mon- 

 tana, hut have not yet been identified by characteristic fossils. 

 2 American Journal of Science, 1878-1884. 



