Geological Society. 519 



the crocodilian type in its greater breadth. The portion exposed 

 in this block is principally convex, but it becomes concave towards 

 the opposite or median margin. At its broadest part it is thirteen 

 inches across, and its length is seventeen inches. This expanded 

 extremity is rounded, and the diameter of the corresponding ex- 

 panded extremity of the ischium, which is obliquely truncated, is 

 nine inches. In another block of stone the expanded extremity of 

 the opposite pubis is preserved, and measures fourteen inches across 

 and twenty-two inches in length. 



The bone, considered by Mr. Owen to be a coracoid, is two feet 

 in length and seventeen inches in its greatest breadth, and it varies 

 in thickness from three to five inches. The breadth of this bone in- 

 dicates, the author states, the great development of the muscles de- 

 stined for the movement of the fore-leg, whence he infers that the 

 anterior extremities were more powerfully and habitually used in 

 progressive motion than in the Crocodiles, and that they were con- 

 sequently provided with a webbed modification of the hand. 



Mr. Owen then enters upon the question of the identity or affini- 

 ties of the Hythe remains with any of the known marine genera of 

 the saurian order, the texture of the long bones being conclusive 

 against their having belonged to the terrestrial genera, the Iguano- 

 don and Megalosaurus. 



The length, thickness, and indications of condyles in the femur, 

 and the length, thickness, and angular form of the metatarsal bones, 

 place, he says, the Plesiosaurus and the Ichthyosaurus out of the 

 pale of comparison ; as well as the Mosasaurus, the locomotive ex- 

 tremities of which are considered to have been flattened paddles. 



The superior expanse of the pubis and the broad coracoid (?), with 

 the form of the femur and the gigantic proportions of the bones, for- 

 bid a reference to any subgenera, recent or extinct, of the crocodilian 

 reptiles ; and he shows that it is distinct from the Poikilopleuron of 

 M. Deslongchamp by the long bones of that Saurian having medul- 

 lary cavities. 



Saurian Teeth from the Lower Greensand. — These teeth, described 

 by Mr. Owen in his ' Odontography ' under the name of Polypty- 

 chodon, are characterized by the crown presenting numerous closely 

 set longitudinal ridges, which are continued, of nearly equal length, 

 to near the apex of the crown. In their size and simple conical form 

 the teeth of the Polyptychodon resemble those of the great sauroid 

 fish, Hypsodon, Ag., but may be distinguished by the solid compact 

 structure of the dentine, which is resolved by decomposition into 

 successive cones ; and also by the ridges on the exterior of the crown 

 of the Hypsodon' s teeth being alternately long and short, and ter- 

 minating abruptly at different distances from the base, the interspaces 

 between the longer ridges widening as they approach the apex. The 

 tooth of the Polyptychodon is slightly and regularly curved, and in- 

 vested with a layer of enamel of a clear, amber-brown colour, and of 

 which the ridges are composed, the surface of the outermost layer 

 of dentine being smooth. A tooth from the lower greensand near 

 Maidstone has a crown three inches long, and one inch four lines 



