94 0. C. Marsh — Notice of a New Fossil Sirenian. 



The astragalus is 55 mm in width ; and 50 mm in fore and 

 aft diameter. 



A first phalanx of the hind foot is 90 mm in length. 



These specimens would indicate an animal ten or twelve feet 

 in length. 



These remains are from the same horizon and localities as 

 those above described. 



Gcelurus gracilis, sp. nov. 



The smallest Dinosaur found in these deposits is a very di- 

 minitive carnivore, apparently belonging to the genus Ccelurus. 

 It was not more than one-half the size of the western species, 

 and its proportions were extremely slender. The bones are 

 very light and hollow, the metapodials being much elongated, 

 and their walls extremely thin. An ungual phalanx of the 

 manus measures about 25 mm in length ; and 14 mm in vertical 

 diameter at the base. 



This animal could not have been more than five or six feet 

 in length. The known remains are from the same horizon as 

 those above described. 



All the specimens described in the present article were 

 found by Mr. J. B. Hatcher, of the U. S. Geological Survey, 

 and the writer's able field assistant in paleontology. 



The fossils here described, and others from the same horizon, 

 seem to prove conclusively that the Potomac formation in its 

 typical localities in Maryland is of Jurassic age, and lacustrine 

 origin. There is evidence that some of the supposed northern 

 extensions of this formation, even if of the same age, are of 

 marine, or estuary origin. 



Tale College, New Haven, Conn., Dec. 23, 1881. 



Art. TIL — Notice of a New Fossil Sirenian, from California; 

 by O. C. Marsh. 



Iisr exploring a Tertiary deposit in California a few years 

 since, the writer obtained several teeth of a large mammal, very 

 distinct from anything hitherto discovered in this country. 

 Other specimens were subsequently secured, and with, them, 

 a number of vertebrae, apparently pertaining to the same ani- 

 mal which is described below. The associated vertebrate fos- 

 sils were a large edentate (Morotherium), a mastodon, a camel, 

 and one or more extinct species of the horse, all indicating the 

 Pliocene age of the strata in which they were entombed. 



