134 PROCEEDINGS OF THE PALEONTOLOGICAL SOCIETY 



originated in some such way and that other multilamellar organisms owe their 

 growth to similar methods. 



All account of American rhinoceroses and the evolution of one genus, 

 well illustrated by lantern slides, was next presented b}^ the author. Dis- 

 cussion by Messrs. Loomis and Matthew. 



AMERICAX RHIXOCEROSE^ AXD THE EVOLUTIOX OF DICERATHERIUM 



BY E. S. TROXELL 



(Abstract) 



Scarcely anj' animal seems more exotic to America than does the rhinoceros. 

 Limited at present to Asia and Africa, we have every reason to believe that 

 they originated in America, In our own continent we can trace the line or 

 lines of descent from H yrachijus and allied forms of the middle Eocene through 

 to the Pliocene, where the family becomes extinct. Horns were developed in 

 the earlj' Miocene, but their incipient beginning is noted in the Eocene. Dicera- 

 thefium, the "two-horned beast" described by Marsh, is clearly related to 

 CamopKs, and by gradual steps its change from that genus can be traced until 

 it reached its splendid development in the late Oligocene. This alone offers 

 convincing proof of the law of evolution. 



The following papers were then read by title 



PRESENT STATUS OF THE OZARKIAX AXD CAXADIAX SYSTEMS 



BY E. O. UDRICH 



MARINE EOCEXE HORIZONS OF WESTERN NORTH AMERICA 



BY BRUCE CLARK 



SOOKE FORMATION OF SOUTHERN YANCOVYER ISLAND 

 BY BRUCE CLARK AXD RALPH ARXOLD 



EVOLUTION OF STROPHEODONTA DEMISSA (CONRAD) IN THE SNYDER 

 CREEK SHALES OF MISSOURI 



BY E. B. BRAXSOX AXD JAMES S. WILLIAMS 



(Ahstract) 



The evolution discussed in this paper took place while 30 feet of shales were 

 being deposited. At the base t>f the Snyder Creek shales ^tropheodonta de- 

 missa (Conrad) showed variational tendencies in the following directions: 

 tow^ard long hingeline and short hingeline ; thick shell and thin shell : great 

 convexity and flatness : fine plications and coarse plications ; strongly project- 

 ing umbo and retreating umbo: narrowness and great width; well developed 

 fold and sinus. 



