Maryland Geological Survey 189 



to one species. They differ somewhat in size, owing, apparently, to a 

 difference in age. 



" In comparing these remains with the Sauropoda now known, they 

 appear to resemble most nearly those of the genus Morosaurus, so well 

 represented in the Upper Jurassic of the Eocky Mountain region. A 

 careful comparison, however, shows that they belong to a distinct genus. 

 The teeth are of the same general type as those of Morosaurus, but their 

 crowns are mainly compressed cones, and not spoon-shaped. The dentary 

 bone is slender and rounded at the symphysis, instead of having the mas- 

 sive, deep extremity seen in Morosaurus. The maxillary is also lighter, 

 and less robust. The supra-occipital agrees closely in shape with that 

 of Morosaurus, and forms the upper border of the foramen magnum, as 

 in that genus. 



" The cervical and dorsal vertebrae are elongate, and strongly opistho- 

 coelous. The latter are much longer than the corresponding vertebrae 

 of Morosaurus, and have a very long, deep cavity on each side of the 

 centrum, to which the proposed generic name refers. All the trunk 

 vertebrae hitherto found are proportionately nearly double the length of 

 the corresponding centra of Morosam'us, and the lateral cavity is still 

 more elongate. These points are shown in the posterior dorsal vertebra, 

 represented in figs. 1 and 2. The neural arch in this region is lightened 

 by cavities, and is connected with that of the adjoining vertebrae by the 

 diplosphenal articulation. 



" The sacral vertebrae in Pleuroccelus are solid, as in Morosaurus, but 

 much more elongate. The surface for the rib, or process which abuts 

 against the ilium, is well in front, more so than in any of the known 

 Sauropoda. Behind this articular surface is a deep pit, which somewhat 

 lightens the centrum. These characters are seen in the sacral vertebra 

 represented in figs. 3 and 4. The first caudal has the centrum very short, 

 and its two articular faces nearly flat, instead of having the anterior sur- 

 face deeply concave, as in the other known Sauropoda. The neural spines 

 in this region are compressed transversely. The middle and distal 

 caudals are comparatively short, and the former have the neural arch 

 on the front half of the centrum, as shown in figs. 5 and 6. The bones 



