410 ROY L. MOODIE 



and inactive types of reptiles, are probably due to the absence 

 of an osteolytic agent, which, in other animals, produces the 

 medullary cavity of adults. The primary medullary cavity 

 of the plesiosaurs, due to the inroad of the branches of the 'perio- 

 steal bud' becomes obliterated, as do all other growth charac- 

 ters, i.e., canal, foramen, groove, and rugosities, very late in 

 life, thus furnishing an interesting instance of the persistence, 

 in the Mesozoic reptiles, of characters which at present are found 

 to occur in modern mammalian embryos. 



BIBLIOGRAPHY 



BiDDEH, Alfred 1906 Osteobiologie. Archiv fi'ir mikros. Anatomie, Bd. 



06. 137-210. 

 Jackson, C. M. 1904 Zur Histologie und Histogenese des Knochenmarkes. 



Archiv fiir Anat. u. Physiol., Anat. Abth., Jahrg. 1904, p. 33. 

 KiPRiJANOFF, W. 1882 Studien liber die fossilen Reptilien Russlands. Mem. 



de I'Acad. Imp. des Sci. de St. Petersburg, VIII Series, pt. II. 

 Lydekker, Richard 1889 Catalogue of the fossil Reptilia and Amphibia, 



vol. 2, p. 149. 

 MooDiE, Roy L. 1908 Reptilian epiphyses. Amer. Jour. Anat., vol. 7, no. 



4, pp. 443-467. 



1911 Trans. Kans. Acad. Sci., pp. 99-100. 

 SzYMONOvvicz, L. 1902 A text-book of histology and microscopic 'anatomy 



of the human body, Trans, by MacCallum, p. 270. 

 WiLLisTON, S. W. 1903 North American Plesiosaurs, Field Museum Pub- 

 lication No. 73, pp. 73-74. 



1914 Water reptiles of the past and present, Chicago, p. 88. 

 WiLLiSTON, S. W. AND MooDiE, RoY L. 1913 A new plesiosaurian Genus from 



the Cretaceous of Kansas. Bull. Geol. Soc. America, vol. 24, no. 1, 



pp. 120-121. 

 Woodward, Arthur Smith 1898 Vertebrate paleontology, Cambridge, p. 170. 



PLATE 1 



explanation of figures 



1 Propodial (humerus) of Ogmodirus martinii, Williston and Moodie, from 

 the Cretaceous of Kansas X 0.5 'S' = tooth marks of some predaceous fish or rep- 

 tile of the Cretaceous seas. 



2 Distal articular end of the humerus of the Ogmodirus showing 'A' the 

 details of the small 'volcanoes' the ends of the 'Canales ossificantes perforantes.' 

 X 0.75. 



3 Cross-section of the femur (fig. 1) showing the foramen, canal and cal- 

 cite-fiUed cavity. The bone structure radiates from the calcite-filled medullary 

 cavity. X 1. 



4 Proximal end of the humerus of Ogmodirus, showing growth characters 

 'A' in the form of small volcano-like eruptions. X 0.75. 



