Cope.] 140 [jlay 15, 



dense laj^er, a light spongy layer, and a very thin inferior dense layer. 

 There were no horny scuta, and it is doubtful whether there were any 

 dermal sutures. The surface is marked with numerous tuliercles which 

 are of elongate form, and run in various directions, frequently inoscu- 

 lating and separating generally narrow fosste. They are finer and more 

 nearly parallel on the distal part of the costal than on the proximal, and 

 they turn at right-angles to the intercostal sutures. The proximal part 

 of the costal is crossed by an angular keel which runs parallel to the 

 middle line of the carapace. It is smooth, interrupting the sculpture. 

 There are therefore two low parallel keels on the superior part of the 

 plastron. AVhether there is a median keel cannot be determined, as no 

 vertebral bone is preserved. At one side of this keel ('?proximad) is a 

 smooth shallow groove, which may represent the border of a vertebral 

 scutum. Not enough of it is preserved to demonstrate its nature. 



The shaft of the humerus is flat in the plane of the distal extremity 

 and is nearly straight, except that it bends a little downwards proximad 

 of the distal extremity of the deltoid crest. The latter descends low on 

 the shaft marking one-third the leugth. Its inferior portion is recurved 

 inwards towards the head. The long axis of the head is at right angles 

 to that of the shaft. The radial process is prominent, and marks two- 

 fifths the length of the shaft from the head on the internal edge. The 

 straight line of the axis of the humerus reaches the distal extremity be- 

 tween the condyles and the entepicondylar foramen. Thus the con- 

 dyles are turned slightly ectad. The internal portion of the condyle has 

 a greater anteroposterior diameter than the external, and though the 

 articular surface is convex anteroposteriorly, transversely there are 

 three shallow concavities, one external and two internal. The internal 

 epicondyle is wide and flat, and equals the condyles in transverse 

 diameter. The external epicondyle is little prominent. The entepicon- 

 dylar canal is oblique, entering nearer the inner margin l)elo\v, and 

 issuing at about the middle above. 



Meusurements. mm. 



Proximal width of costal 1 47 



Thickness of do. at margin 7 



Width of costal 2, at distal end GO 



Thickness of do. at distal margin 3 



Leugth of humerus 100 



-p.. , ,. , T ( anteroposterior 32 



Diameters ol head ■ '■ 



i transverse 1 < 



"Width of humerus distally 41 



Transverse extent of condyles 22 



Length from radial process to distal end 53 



I obtained the specimens al)ove described from a Neocene bed on the 

 Pamunky river, Virginia. It was associated with the Mesocetus siphun- 

 culus Cope, and various species (jf Plalanistid;e, and a S(pialodon. 



