MORPHOLOGICAL REVISION 



III 



shaft. The lower end is wide, but very thin. The entepicondylar process 

 is proportionately wide; the outer part of the distal face is thickened and 

 bifurcated, giving it a U-shaped section, the arms of the U being the termina- 

 tions of narrow ridges from the shaft. There are no faces for radius or ulna. 



K femur. No. 4584 Am. Mus., in all probability belonging to Trimero- 

 rhachis, has the two ends oval and nearly parallel. The shaft is narrow and 

 rounded. On the posterior surface, near the proximal end, is a strong rugose 

 process with the end cupped like the ends of the bone, showing cartilaginous 

 attachment. The lower end of the process is continued as a thin ridge, which 

 narrows to a line running nearly to the distal end of the bone. The lower 

 face of the femur is roughly divided by a constriction near the middle. The 

 outer part is wider than the inner, but there are no distinct faces for tibia 

 and fibula. 



Another femur (bearing the same number) is of a slightly different form. 

 The upper and lower ends are parallel, but the process on the posterior face 

 is not separate from the bone; it is continuously attached to it and its upper 

 face is a part of the proximal face of the bone. The end is similar to the 

 first described. 



Fig. 42. 



A. Trimerorhachis sp. No. 4720 Am. Mus. X i- Humerus of right side, posterior view. 



B. Same humerus, anterior view. 



C. Trimerorhachis (?) sp. No. 4584 Am. Mus. X 4- Small femur probably belonging to Trimerorhachis. 



D. A second, larger femur. 



E. Trimerorhachis (?) sp. X 4- A small ilium in the collection of the American Museum belonging to 



TrimeTOrhachis or possibly to Zatrachys. a, from outer side; b, from inner side. 



Certain small ilia found in the bone beds belong either to Trimero- 

 rhachis or Zatrachys; it is probable that there was little difference in the axial 

 skeletons of these forms. The upper end of the ilium is thick and expanded 

 in fan shape; the inner surface is marked with radiating lines, the outer face 

 concave. The shaft is rather elongate and slender. The lower end is ex- 

 panded to take part in a good-sized cotylus. The three bones of the pelvis 

 were apparently strongly united. 



Trimerorhachis is not yet sufficiently well known to attempt a restora- 

 tion or a description of its probable habits. The extremely large notochordal 

 space left between the elements of the vertebrae and the phyllospondylous 

 condition of the anterior vertebrae proclaim it as the most primitive form of 

 Amphibia from Texas. 



