Geological Papers. 95 



AN EMBRYONIC PLESIOSAURIAN PROPODIAL. 



By Roy I_ Moodie. Unrrersnj of Ka-.sa.'. 



/^UR conception of the morphology of vertebrate limb bones is 

 ^^ much complicated by the conditions found in the propodials 

 of embryonic and young plesiosaurs. Examples of these bones are 

 not at all rare in the Cretaceous deposits of the West, and there are 

 several references to them in the literature, including a few discus- 

 sions of the characters which they present. Doctor Williston has 

 especially dwelt upon the characters of a very immature plesic- 

 sanrian limb bone which he discovered in the chalk of western 

 Kansas. He also figured examples of other, more mature, propo- 

 dials ( Field Museum. Publication 73. plates 22 and 23, 1V^3 (. The 

 writer later referred to the immature element and described others 

 in an attempt to arrive at some conclusions in regard to the mor- 

 phology of the so-called epiphyses of the plesiosaurs (Amer. Journ. 

 Anat., vol. VII, No. 4, p. 443. IVOS). The conclusions reached 

 pointed definitely to the fact that the so-called epiphyses of plesio- 

 saurs, turtles and dinosaurs are in reality the endochondral ossifica- 

 tions of the limb bones, and differ in all structural respects from 

 true epiphyses. 



The conditions which complicate our conceptions of the mor- 

 phology of the vertebrate limb bones are the presence of numerous 

 grooves and foramina in many places on certain types of plesio- 

 saurian propodials. These grooves and canals are especially well 

 marked in the specimen which is described herewith. 



There has been in the museum of the University of Kansas for 

 some time a small embryonic plesiosaurian propodial which I sup- 

 pose to represent a humerus. It is as immature as any propodial 

 known to me. with the exception of the small one described by 

 Doctor Williston. Judging from the matrix still adhering to the 

 specimen, it is from the Niobrara Cretaceous, but just what locality 

 is not known, though probably somewhere in western Kansas. The 

 element presents most peculiar and unusual characters, which are 

 believed to be new to our knowledge of plesiosaurian anatomy. 

 The character which is especially striking is the deep, well-marked 

 groove on the radial (?) side. It forms, save for a small pathologi- 

 cal interruption, a shallow, smooth-bottomed trough which extends 

 fully half around the periphery. On the opposite edge there is a 

 very shallow groove which is not nearly so well marked as the one 



