180 KANSAS UNIVERSITY QUARTERLY. 



the crown is convex, to correspond with the concavity of the uj^iDer 

 dental plate, and the ridges are directed like them, but are shorter and 

 rather less strong. The ridges, furthermore, extend very nearly to 

 the inner margin, not fading out at some distance from it as do they 

 in the upper plate. There are eight ridges, corresponding to the 

 grooves of the upper plates. The grooves are deeper outwardly than 

 are the upper grooves. The plate altogether is more slender than the 

 ui^per ones. 



The splenial plate has been figured in union with a mate in a posi- 

 tion to correspond with the up^jer plates, and the other bones of the 

 mandible are outlined from Ceratodus. (PI. xxxvii, fig. 1.) 



Several large and well-ossified bones of an oval-concave shape are 

 present in the rocks. Several of them have been removed nearly com- 

 plete, and are shown in plates xxviii, xxxv, and xxxvi. They resemble 

 not a little a valve of a pelecypod. The outer surface is strongly 

 convex, one end more or less sharply truncate, the lower border 

 strongly convex, the upper border with a fiattened tooth-like process, 

 on either side of which the border is more nearly straight. The bor- 

 der everywhere is thin, the inner surface concave, and there are no 

 indications of sutural attachments, unless it be on the truncated end. 

 It would seem probable that the bone is an opercular, although there 

 is no surface indicated for the attachment of the subopercular. 



Another bone, that may be the subopercular, is of smaller size than 

 the foregoing. (PI. xxxvi, fig. 3.) It is somewhat fan-shaped in out- 

 line, the outer surface convex, the border thin, the inner surface con- 

 cave. The inferior lateral border is nearly straight, meeting the 

 expanded border nearly in a right angle ; the other lateral border is 

 strongly convex, and is inflected inward; on the convex surface there 

 is a convex depression on the inflected portion. The surface between 

 this line and the convex border evidently was in apposition to some 

 other bone, i^erhaiDS the preceding. 



A bone, which from its resemblance to the ceratohyal of Ceratodus 

 may be that, is shown in plate xxviii, figures 3, 3a, and 3 J. The upper 

 end is oval, truncated squarely, and with a deep conical cavity, reach- 

 ing nearly to the middle of the bone, the bone itself being merely a 

 shell. The lower extremity, more elongated, is also deeply hollow. 

 The border rejjresented in figure Za is broadly rounded. Near the 

 middle of the surface shown in figure 3 there is a vertical, rather 

 sharp ridge, standing out abruptly from the bone, and evidently for 

 muscular or cartilaginous attachment. On the other surface a thin 

 flat plate extends obliquely backward from the bone. Its whole ex- 

 tent is not preserved. Three or four of these bones are preserved in 

 the collection, but none are complete. 



