This is the most frog-like, in appearance at least, of all the Amphibia which have so far been discovered in the Carboniferous. The skull especially has a shape which is strikingly frog-like, and the long hind limbs lend further likeness to the tailless forms. _Pelion_ may have been a jumping creature, if we may judge from its long hind legs. Wyman and Cope have both called attention to the frog-like appearance of the specimen, and this is apparent at the first glance. It is probable that the resemblance has some significance as to the ancestry of the Salientia, and it may indicate the first step in the origin of the tailless Amphibia. It is possible that the frogs began to be separated from the other Amphibia during the Carboniferous. The first frogs we know are from the Jurassic, where they are well-developed ranids. If _Pelion_ be a frog ancestor, then the history of the group from the Coal Measures to Jurassic is an unknown story. The specimen is preserved on its back and it is thus impossible to tell as to the structure of the skull. Cope was of the opinion that the depressed areas on the sides of the elongate parasphenoid were the orbits, and if so the resemblance to the frogs is much more striking. In the frogs there is a strong process from the pterygoid which projects inward to meet a corresponding process from the parasphenoid. This forms a heavy rod behind the palatine vacuity. There is a heavy rod represented in the specimen and a part of it is certainly the external process of the parasphenoid, but whether it is to be interpreted as in the frog is an open question. The outline of the cranium is partially obscured by the mandibles, but the anterior part is represented by a raised line, as shown in figure 17. In the anterior part of this space there are two ridges which may be tooth ridges. If they are teeth there is a great similarity to the premaxillary and vomerine teeth of _Necturus_, since the ridges are widely separated at the median line and approximated distally, as they are in _Necturus_. The mandible is preserved entire and its form is strikingly frog-like. Its posterior angles project over the quadrate area and seem to have had an upturned projection such as is found in the mandibles of the Crocodilia. There are impressions of 20 vertebræ preserved, and they cover a little more than half of the presacral region. There may have been 28 to 30 presacrals. The vertebræ, as preserved, are somewhat quadrate in outline and constricted at the middle, as though they were of the typical microsaurian type. No ribs are preserved. [Illustration: Fig. 17. _Pelion lyelli_ Wyman, an amphibian from the Coal Measures of Ohio, the supposed ancestral salientian. (After Wyman.) × 0.75. _pmx_, premaxilla; _pv_, palatine vacuity; _m_, mandible; _sc_, scapula-coracoid; _h_, humerus; _r-u_, radius and ulna; _f_, femur; _t_, tibia.]