110 DINOCERATA. 



Measureiuents uf Right Pisiform. [Dinoceras mimbile, Xo. 1211.) 



m. 



Length of pisiform bone, _ -06 1 



Greatest transverse diameter, ._ -050 



Least transverse diameter, — — 030 



Greatest diameter of ulnar articular surface, .038 



Least diameter of ulnar articular surface, .02 1 



Greatest diameter of face for pyramidal, . _ .047 



Least diameter of face for pyramidal, — - -- .029 



Meiisuremeuts of Right Pisiform. {Binoceras mirabile, No. 1520.) 



m. 



I .ength of pisiform bone, -065 



Greatest transverse diameter, 045 



Least transverse diameter, .033 



Greatest diameter of ulnar articular surface, .042 



Least diameter of ulnar articular surface, . - 021 



Greatest diameter of face for pyramidal, .044 



Least diameter of face for pyramidal, .023 



The Trapezium. 



(Plate XXXIII, figures 1-G, and Plate, LIV, figure 1, tm.) 

 The trapezium in the IHnocerata is well developed, being 

 considerably larger than the trapezoid. It presents at each end a large 

 articular face, and a third smaller and much less regular one, for 

 articulation with the trapezoid, on the side turned toward that bone. 



The outer, or dermal, surface of the bone (Plate XXXIII, figure 1), 

 when viewed in its natural position in the foot, is rough and tuberculated. 

 The p< sterior view (figure 2), and the anterior view (figure 4), likewise 

 show no articular faces. Figure 3, representing the sui'face turned toward 

 the trapezoid, presents an in-egular, smooth face along the upper margin. 

 This face diff'ers in size and proportions in different specimens, and in life 

 moved upon a corresponding surface on the trapezoid. 



The proximal end of the bone (figure 5) is almost entirely covered by 

 the articular face for the scaphoid. This face, nearly semi-circular in 

 outline, is flattened in one direction, slightly concave in the other, and 

 confluent along the straight margin with the face for the trapezoid. 



