402 ROY L. MOODIE 



surfaces have not developed distinct facettes; the mesopodial 

 elements are rounded and incomplete as though imbedded in 

 a mass of cartilage, as well as the presence of growth characters 

 which, heretofore, have been found only in young or embryonic 

 bones. The species of plesiosaur referred to has been described 

 as Ogmodirus martinii and the animal may have been twelve, 

 to fifteen feet in length, which, in comparison with other mem- 

 bers of its family (the Elasmosauridae) is not long. The Plesio- 

 sauria included some of the largest aquatic reptiles which have 

 ever existed, equaled perhaps, though not exceeded by some 

 of the extinct crocodiles. The largest known are probably 

 those of the Kansas chalk, or the Jurassic of Wyoming, which 

 probably reached a length of nearly or quite fifty feet, of which 

 the neck formed about one-half (Williston, '14). 



The elements of this incomplete skeleton which concern us 

 here are the humerus, the femur and the phalanges. These 

 are the only elongate bones of the limbs, the other elements 

 being rounded plates (text fig. 1). In one of these, the femur, 

 the bone has been broken a,cross the plane of the medullary 

 cavity, exhibiting the internal structure of the bone at this place 

 (plate 1, fig. 3 and text fig. 4). The foramen, which is clearly 

 evident from a lateral view of the bone, leads into an elongate 

 canal, which, in turn, opens into an enlarged medullary cavity, 

 which is filled with calcite in the specimen, and from this 

 cavity the bone structure (plate 1, fig. 3) radiates in all direc- 

 tions. The outlines of the medullary cavity are not regular, but 

 present many sharp pointed indentations which have been inter- 

 preted as being the places of exit of the Canales ossificantes 

 perforantes. 



The ends of the limb bones are covered with curious pits and 

 cones which resemble miniature volcanoes 'A' (plate 1, figs. 2 

 and 4). The significance of these curious structures is sug- 

 gested below. They are confined to immature bones. It has 

 been generally assumed that all of these unusual characters 

 mentioned above have been confined to the propodium, but, 

 in studying the osteology of Ogmodirus it was noted that the 

 phalangeal bones exhibited the foramina, canals and cavities, 



