92 0. C. Marsh— New Genus of Sauropoda. 



The bones of the limbs and feet preserved, agree in gene- 

 ral with those of the smaller species of Morosaurus, but indi- 

 cate an animal of slighter and more graceful build. The 

 metapodials are much more slender, and the phalanges are less 

 robust than in the other members of the order. 



The known remains of the present species, representing sev- 

 eral individuals, indicate an animal not more than twelve or 

 fifteen feet in length, and, hence, the smallest of the Sauro- 

 poda. They were found at several localities of the Potomac 

 formation in Prince George Co., Maryland. 



Regarding the present species as typical, some of the more 

 special characters distinguishing these remains from the known 

 Sauropoda are as follows : 



(1) Teeth with compressed, or flattened crowns. 



(2) Dorsal vertebrae with low neural sutures, and elongate 

 excavation in each side of centrum. 



(3) Sacral vertebrae solid, with cavity in each side, and with 

 face for rib in front. 



(4) Anterior caudals with flat articular faces, and transversely 

 compressed neural spines. 



(5) Middle caudal vertebrae with neural arch on front half 

 of centrum. 



These characters appear to indicate a distinct family, that 

 may be called the Pleurocodidce. 



Pleuroccelus alius, sp. nov. 



A larger species apparently of the above genus is represented 

 by various remains from the same localities as the specimens 

 just described. A tibia and other limb bones show the ani- 

 mal to have had elongated posterior extremities, at least a third 

 longer, proportionately, than in Morosaurus, which these re- 

 mains, in some respects, clearly resemble. 



The tibia has the proximal end compressed transversely, with 

 its outline sub-rhomboidal. The cnemial crest is well devel- 

 oped. The shaft is solid throughout, with the exception of a 

 very small cavity near the middle, and here it is sub-ovate in 

 trausverse section. The distal end is much flattened antero- 

 posteriorly, and the notch in the articular face, characteristic of 

 the Sauropoda, is well marked. This tibia is twenty-five 

 inches (M. "635) in length, with its proximal end seven inches 

 (M. -177) in fore and aft diameter, and the distal end six inches 

 (M. •152) in transverse diameter. Both extremities are rugose, 

 indicating a heavy covering of cartilage. The fibula is mas- 

 sive, and its distal end somewhat expanded. The astragalus 

 was free, and is wanting in the present specimen. 



