206 Mr. Owen on the Fossil Remains of a Mammal 



of the extremely rare Pachydermal genus Chceropotamus, to which the Hyracothe- 

 rium bears the closest affinity. 



PI. XXL Fig. 1 to 4. 



Fig. 1. View of the palatal surface of the skull and of the grinding surface of the molar teeth of the 

 Hyracotherium leporinum, natural size. 



Fig. 2. View of the upper or coronal surface of the same. 



Fig. 3. Side view of the same. 



Fig. 4. The series of molar teeth, with the socket of the canine of the right side of the upper jaw, mag- 

 nified two diameters. 



Ornitholite. (Lithornis vulturinus, PI. XXI. Fig. 5 and 6.) 



The evidence of the coexistence of Birds with Mammals in the English Eocene 

 tertiary formations rests upon two Ornitholites, including the most characteristic 

 parts of the skeleton of a bird, viz. the sternum and sacrum ; both these fossils 

 are from the London clay at Sheppey. The first forms part of the extensive col- 

 lection of organic remains which the celebrated John Hunter left at his decease, 

 and I have availed myself of the permission granted me by the Museum Committee 

 of the Royal College of Surgeons to describe it in connexion with the Mammalian 

 fossil from the same formation already adduced in the present paper. 



The second Ornitholite, consisting of the sacrum and part of the coccyx, is from 

 the museum of Mr. Bowerbank, which is well known to be peculiarly rich in 

 Sheppey fossils. 



The Hunterian fossil (Fig. 5,6.) includes the sternum nearly entire, the proximal 

 ends of the coracoid bones, a dorsal vertebra, the distal end of the left femur, the 

 proximal end of the corresponding tibia, and a few less characteristic fragments of 

 ribs ; all these bones are cemented together by the grey indurated clay which is ge- 

 nerally more or less attached to the Sheppey fossils. A single glance at this cha- 

 racteristic specimen is sufficient to assure the comparative anatomist of the class 

 of animals to which it belongs. The next question that arises is, to which of the 

 three great primary groups of Birds the fossil is to be referred ? Whether to the 

 aquatic, the terrestrial, or the aerial birds of the philosophical ornithologist, 

 Nitzsch ? 



The length of the sternum and the remains of the primary intermuscular crest 

 or keel forbid a reference of the fossil to the Struthious or strictly terrestrial order, 

 but at the same time do not prove so decidedly, as might be supposed, that the 

 fossil must have belonged to a bird of flight. 



The Penguins and other Brachyptera, having need of muscular forces to work 

 the wings as paddles while making their way under water, almost equal to those 



