Pro/. 0. C. Marsh — A New American Jurasaic Dinosaur. 101 



nasal aperture (c), the orbit {d), and the lower temporal opening {e) 

 (Figure 2). The first of these has not been seen in any other 

 Dinosaur ; the large antorbital vacuity is characteristic of the Sauro- 

 poda ; and the other three openings are present in all the known 

 Ditiosauria. 



On the median line, directly over the cerebral cavity of the bi'ain, 

 the type specimen of Biplodocus 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 fronto-parietal surface. 



The occipital condyle is hemispherical in form, and seen from 

 behind is slightly sub-trilobate in outline. It is placed nearly at 

 right angles with the long axis of the skull. It is formed almost 

 wholly of the basi-oecipital, the exoccipitals entering but slightly or 

 not at all into its composition. The basi-occipital processes are large 

 and rugose. The paroccipital processes are stout, and somewhat 

 expanded at their extremities, for union with the quadrates. 



Fig. 3. — View of the skull of D. longus, as seen from above (one-sixth nat. size). 



The parietal bones are small, and mainly composed of the arched 

 processes which join the squamosals. There is no true parietal 

 foramen, but in the skull here figured 3 there is the small unossified 

 tract mentioned above. In one specimen of Morosaurus, a similar 

 opening has been observed, but in other Sauropuda, the parietal 

 bones, even if thin, are complete. The suture between the parietals 

 and frontal bones is obliterated in the present skull, and the union is 

 fii'm in all the specimens observed. 



The frontal bones in Biplodocus are more expanded transversely than 

 in the other Sauropoda. They are thin along the median portion, but 

 quite thick over the orbits. 



The nasal bones are short and wide, and the suture between them 

 and the frontals is distinct. They form the posterior boundary of 

 the large nasal opening, and also send forward a process to meet the 

 ascending branch of the maxillary, thus forming in part the lateral 

 border of the same aperture. 



The nasal opening is very large, subcordate in outline, and is par- 

 tially divided in front by slender posterior processes of the pre- 

 maxillaries. It is situated at the apex of the skull, between the 

 orbits, and very near the cavity for the olfactory lobes of the brain. 



