STRATIGRAPHIC AND GEOGRAPHIC DISTRIBUTION. 13 



Class AMPHIBIA Linne, 1758 Continued. 

 Subclass Lepospondylia Zittel, 1887. 

 Order Microsauria Dawson, 1863. 



Family Amphibamida Cope, 1875. 



Amphibamus grandiceps Cope, 1865. 

 Amphibamus thoracatus Moodie, 191 1. 

 Cephalerpeton ventriarmatum Moodie, 1912. 

 Family Molgophidm Cope, 1875. 



Erpetobrachium mazonensis Moodie, 1912. 

 Subclass Stegocephala Cope, 1868. 



Order Temnospondylia Zittel, 1887. 

 Suborder Embolomeri Cope, 1885. 

 Family Cricotida Cope, 1884. 



Spondylerpeton spinatum Moodie, 1912. 



It will be seen from the above arrangement that nearly all of the orders of 

 Amphibia are represented in the Mazon Creek fauna. These animals are the oldest 

 known land vertebrates of North America. 



Contour interval 50 feet 



FIG. 3. Portion of the "Morris sheet" of the U. S. Geological Survey, to show 

 topography and situations of the exposures of fossil-bearing shales at Mazon 

 River, a, the "Bartlett place," the so-called "upper beds"; b, "lower beds." 



The writer was able, during July 1911, to spend a week studying the fossil beds 

 (479) at Mazon Creek. The object of the visit was primarily to collect Amphibia, 

 but although several thousand nodules were examined, not one contained an 

 amphibian nor a fragment of one. Mr. J. C. Carr, of Morris, Illinois, who has collected 

 at Mazon Creek for more than 30 years, has never collected an amphibian. These 

 facts interested me in making the following comparison: If we take 100,000 nodulrs 

 as a basis for computation of the rarity of the various forms, something like the 

 following will be the approximate result of the investigation: 



