NORTH AMERICA AND THEIR VERTEBRATE FAUNA. 



167 



articular surfaces. The proximal end has a deep bicipital fossa, but lacks 

 any distinct process on the inner side, its place being taken by the upper 

 end of the ridge, v/hich is here sHghtly thickened. The distal face is very 

 similar to that of a Pelycosaurian reptile, being sharply divided into two 

 faces by a deep groove on the anterior face. This bone may very possibly 

 turn out to belong to a reptile when the skeleton is known. 



The second femur (No. 3431, fig. 39, (/, c,f) is similar to the one from the 

 Craddock bone-bed figured by Williston (Amer. Perm. Vert., pi. xxxiii, fig. 4) 

 and by him referred to Broil icU us {A spidosa urns) pellatiis. It is devoid of well- 

 marked articular condyles but has a prominent adductor ridge. It is prob- 

 ably to be associated with the single dorsal plate discovered (No. 3404), 

 described below. Length 53.5 mm. 



The third femur (No. 3295) (plate 23, figs. 5 and 6, and fig. 40, a and b) is 

 also typically amphibian and might be regarded at first as that of a young 

 Eryops, as the articular ends are deeply excavated, indicating the presence of 

 considerable cartilage, but closer study reveals essential differences. The ad- 

 ductor ridge is relatively much higher and thinner than in the adult Eryops. 



Fig. 40. — (a) Proximal face, (b) distal face of unnamed amphibian, No. 3295. X 73. (Articular 

 faces of bone shown in plate 23, figs. 5 and 6.) 

 (c), (rf), {e) Three views of tibia or radius of an unnamed amphibian, No. 3299. X 73. 

 (/) Outer face, (g) anterior edge of ilium of left side of unnamed ampliibian, No. 3430. X 73. 



In the adult of that genus there is a very deep bicipital fossa and its edges meet 

 below in a strong, almost rugose, prominence at about the middle of the shaft; 

 below this the ridge is very thick, with a flat terminal face, and is continued to 

 the distal end of the bone. In the new form the tibial side of the bicipital fossa 

 is a strong ridge which develops at the upper third of the bone into a strong, 

 circular, and rugose tuberosity with a depressed face; below the tuberosity 

 the ridge is very thin, almost a knife-edge, and it terminates a considerable 

 distance above the distal condyles. The articular faces are proportionately 

 larger than in the adult Eryops. Length 98 mm. 



A bone, No. 3299, is probably amphibian and is either a tibia or a radius. 

 The form is best understood from figure 40, c, d, e. Length, 56 mm. 



A small ilium, No. 3430 (fig. 40,/ and g), resembles in many ways that of 

 Eryops and may be that of an immature individual of the genus. There are, 

 however, some important differences. The crest is vertical like that of Eryops, 



