12 



Measurements. m. 



Length of plastron 183 



Length of anterior lobe 049 



Length of bridge 076 



Width of bridge . 076 



Width of extremity of posterior lobe 035 



Thickness at inguinal region ..... .010 



Hedronchus sternbergii, Gen. et sp. nov. 



Char. Gen. — The bone on which this genus reposes has the ap- 

 pearance of the crown of a young tooth. Its central cavity is large 

 and expands to the margin of the basis; its apex is unworn. It 

 appears to be too protuberant for the position of a dermal tubercle. 

 It may be distinguished as a short crown on a shorter slightly 

 constricted portion or neck. The crown culminates in three crests, 

 which together form a letter T, and which descend towards the 

 neck. There is no investment of enamel or cement, and the ma- 

 terial of which it is composed resembles dense bone. 



Char. Specif. — The faces on each side of the stem of the T, are 

 concave and divided by an oblique crest, which descends from the 

 common apex. The other face is gently convex, and the inferior 

 part of each of its bounding crests projects ear-like. The base is 

 an oval. 



Measurements. m. 



Elevation of crown 006 



Diameter of base {longitudinal . . ... . .005 



(.transverse ..... .004 



Discovered by Charles H. Sternberg. 

 Ceratodus erueiferus, sp. nov. 



A basal lamina separable from the dentigerous lamina. The 

 latter supports ribs which diverge from a single marginal rib 

 which extends along one side. The marginal rib is separated by 

 a deep groove from the radiating ribs, which is continuous with 

 the grooves between the latter. The ribs are of irregular diameter 

 and not perfectly straight; they are interrupted by weak trans- 

 verse ridges which project beyond the margins. The ridges rises 

 abruptly from their common base and are separated distally by 

 notches of the margin. 



