R. L. Moodie— Mazon Creek Shales. 277 



Akt. XXVI. — The Mason Creek, Illinois, Shales and their 

 Amphibian Fauna • by Roy L. Moodie. 



The Mazon Creek shales Lave been noted for many years for 

 the excellence of the fossils which are found in them. These 

 fossils are, for the most part, plant remains, but occasionally 

 animal fossils are found, usually in nearly perfect preservation. 

 Among the vertebrates which have been recorded from these 

 beds are about twenty-five species of elasmobranch, dipnoan, 

 crossopterygian and acanthopterygian fishes. Nine of these 

 species are founded on scales and will doubtless be subjected 

 to revision later. Other vertebrates are represented in the 

 amphibian fossils, of which there are, at present, ten species 

 known. These ten species are distributed among eight genera, 

 five families and four orders ; thus showing the amphibian 

 fauna of the Mazon Creek shales to be a diverse one. This 

 diversity undoubtedly indicates a long antecedent history for 

 the group. The genera and species, even nearly all of the 

 families, are exclusively Mazon Creek forms, not being known 

 from elsewhere in the world. From this we know that in the 

 Pennsylvanian the Amphibia were already a sufficiently old 

 group to have established themselves into distinct, widely sepa- 

 rate geographic groups. Just how long it may have taken for 

 them to so establish themselves is, of course, a matter for con- 

 jecture. 



The larger amount of the material representing the amphib- 

 ian fauna of the Mazon shales is in the Yale University Mu- 

 seum, where it had been gathered by Professor Marsh. The 

 writer is indebted to the authorities of the Museum for the 

 privilege of studying this interesting collection. Seven of the 

 species of the Mazon Creek Amphibia are known only in this 

 collection at Yale. Seven of the species are founded on con- 

 siderable portions of the skeleton, and some of them show 

 many soft parts as previously described by the writer. * Two 

 species are known from nearly complete remains of three indi- 

 viduals. The ten species are as follows : 



1. Amphibamus grandiceps, Cope, 1865. Three nearly com- 

 plete specimens. 



2. Amphibamus thoracatus, Moodie, 1911. One incomplete 

 specimen. 



3. Micrerpeton caudatum, Moodie, 1909. One complete indi- 

 vidual. 



4. Eumicrerpeton parvum, Moodie, 1910. Three nearly perfect 

 forms. 



* American Naturalist, xliv, p. 367, 1910. 



Am. Jour. Sci.— Fourth Series, Vol. XXXIV, No. 201.— September, 1912. 



