no 



AMPHIBIA AND PISCES OF THE PERMIAN OF NORTH AMERICA 



cally pitted and marked with a reticulate sculpture. The sacral and caudal 

 vertebrae are unknown. 



The ribs of the anterior and middorsal region have heavy, single-headed, 

 proximal ends ; the body of the rib is short and the distal half is expanded 

 into a thin blade. 



The shoulder girdle is known only from the clavicles and interclavicle. 

 The interclavicle, No. 4717 Am. Mus. (plate 12, fig. 2), is a thin rhomboidal 

 plate, with one angle posterior, but not drawn out to a point. The converg- 

 ing posterior edges are thickened and the sculpture is carried out to the 

 edge, making it somewhat rough. The anterior edges are thin where they 

 were overlapped by the clavicles. The sculpture radiates, in a general way, 

 from a point somewhat posterior to the middle of the median line. 



In the bone beds, where the scattered bones of Trimerorhachis occur 

 abundantly, mingled with remains of other creatures, a peculiarly formed 

 plate is of very frequent occurrence; one such is shown in fig. 41 b. 



A similar plate is associated with one of Cope's specimens of Trimero- 

 rhachis and in specimen No. 4866 Amer. Mus., such a plate lies between 

 the lower jaws. It is uncertain whether these are the clavicles or whether 

 they are protective plates normally gular in position. One edge is nearly 

 straight; from this the plate rises in a convex surface and contracts to an 

 apex, which is curved toward the underside of the bone; the whole plate is 

 marked by a sculpture of lines radiating from the apex. 



Fig. 41. 



A. T. insignis. Outline of a rib, showing posterior expansion of blade. No. 4675 



Am. Mus. X J<. 



B. Trimerorhachis sp. Outer view of a plate found in the thoracic or gular 



region. No 125 (Field No.) Am. Mus. X K- 



C. Trimerorhachis sp. Lower view of a small skull, showing such a plate as is 



figured in B, in position as found. No, 4866 Am. Mus. X H- 



Under the No. 4720 Am. Mus. are collected three humeri closely simi- 

 lar to a less perfect one associated with a skull of Trimerorhachis. The 

 ends are turned at an angle of 45° to each other, hardly half as great as in 

 Eryops and Diadectes. 



The articular surfaces are hollow and imperfectly ossified, showing the 

 presence of a large amount of cartilage. The inner side of the proximal end 

 is wider than the outer and the face descends somewhat on the side of the 

 bone; the shaft narrows to a triangular section. The outer edge of this part 

 is interrupted by a stout rugosity, flattened or concave on the surface and 

 not standing out from the bone; it is the homologue of the stout transverse 

 process in the same position on the humerus of Eryops. On the anterior 

 angle there is a slight tuberosity just above where the head narrows to the 



