MOODIE: MAZON CREEK, ILL., SHALES. 329 
Erierpeton branchialis, New Species. 
(Plate 1, fig. 3; plate 2. fig. 1.) 
The amphibian remains which are designated by the above 
name consist of a distinct mandible and some rather indefinite 
body impressions. Three elongate impressions occur between 
the rami of the mandibles, which, I suppose, must represent 
hyoid bones belonging to the branchial arches. The lateral 
elements are paired and the median impression is straight and 
lies between the paired portions of the hyoids. The paired 
portions probably represent the hypohyals, or hypohyals plus 
the ceratohyals, and the unpaired portion the first basi- 
branchial, according to the nomenclature of Wiedersheim 
(Comparative Anatomy of Vertebrates, 1897, p. 86). If the 
impressions have been correctly interpreted, the present speci- 
men is of very great interest since it is the first evidence we 
have of the hyobranchial arches in the Amphibia of Mazon 
Creek, and the second in the Carboniferous of North America. 
Dawson doubtfully identified some elements of the Joggins 
Amphibia as hyoids, but was uncertain as to their position. 
Cope described fully the well-developed hyobranchial apparatus 
of Cocytinus gyrinoides from the Coal Measures of Ohio. 
Among other Paleozoic Amphibia, Williston has described 
branchial arches in the peculiar form Lysorophus tricarinatus 
Cope, from the Permian of Texas. 
The form of the impression of the mandible in the present 
specimen is unlike anything known to the writer among other 
Carboniferous or later Amphibia. The rami are long, slender, 
deep, slightly curved and pointed anteriorly. The anterior 
symphysis was not a complete sutural union, but was occupied 
partly by cartilage or connective tissue. 
There are no definite traces of appendicular structures. 
The traces of the body, plate 2, fig. 1, indicate an elongated, 
rather slender animal, but further than that nothing can be 
said in regard to its structure. 
The occurrence of a typically caudate form in the Carbon- 
iferous is unusual, and complicates still further our under- 
standing of the origin and relationships of the early Amphibia. 
