EDENTATA. 277 



and downwardly curved transverse processes, doubtless originally con- 

 nected by ligament with the rudimentary pelvis ; the caudals are at least 

 twenty-five in number. The sternum even in the adult comprises a series 

 of three separate pieces. The radius and ulna are partially fused together. 

 Two well -developed metacarpals and two phalanges are known, indicating 

 the presence of a manus. The rudimentary pelvis consists of a triradiate 

 bone on each side, displaying a small, shallow acetabular pit ; and the 

 femur is a small styliform bone, a little bent at its stout proximal end. 

 The typical species, Halitherium schinzi (fig. 159), occurs in the Lower 

 Miocene marine deposits in the basin of Mayence, Germany. Other 

 remains of the same or almost indistinguishable genera have been 

 described from Wiirtemberg, Austria, Switzerland, France, Belgium, 

 southern Russia, Italy, Malta, Egypt, and the Pliocene Red Crag of 

 Suffolk. / 



Rhytlna is the largest known Sirenian, sometimes attaining a length 

 of as much as seven or eight metres. It is toothless, displaying only the 

 sockets of a pair of rudimentary incisors in the downwardly curved 

 premaxillae. The head is relatively very small. There are seven cervical 

 vertebrae, nineteen dorsals with ribs, and between thirty and forty verte- 

 brae forming a long tail. The nineteenth rib is a diminutive rudiment. 

 The bones of the hand and rudimentary hind limb are unknown. The 

 only known species, Rhytina stelleri, inhabited the coasts of Behring and 

 Copper Islands, off the coast of Kamtschatka, until late in the last 

 century, and a memoir on the animal was published by Steller in 1751. 

 Fossil skeletons are found in the old raised beaches and peat bogs of this 

 region. 



ORDER 3. EDENTATA. 



The general tendency of palseontological discovery at 

 present is to suggest that the Edentata are not so primitive 

 and isolated a group among the placental mammals as they 

 were commonly supposed to be. It seems that they are rather 

 to be regarded as degenerate types, probably derived from 

 some of the common ancestors of the ungulates and rodents. 

 At least, there are certain imperfectly known genera in the 

 Eocene formations of North America, variously termed T^ENI- 

 ODONTA, GANODONTA, or STYLINODONTIA, which seem to be best 

 interpreted as ancestral Edentates, and these exhibit a decided 

 approach to more normal placental mammals. 



The early North American group just mentioned is charac- 

 terized by the presence of incisors in both jaws, by a typical 

 molar and premolar dentition, and by a trituberculate molar 



