NEW FACTS CONCERNING BOTHRIOLEPIS. 



II/ 



ventro-laterals, as far as the large transverse ridge on their inner 

 surface, to which it seems to be attached. It extends across the 

 median line without interruption except between the mandibles. 

 It also appears to be absent between the mandibles and maxillae, 

 Figs. 2 and 3, 0.111, 



The mandibles are thin, concave plates of bone, continuous 

 with the oral membrane on the sides and in front, but with free 



ynd 



FIG. 3. Ventral side of head, with the anterior ventro-laterals removed on one 

 side, to show extension backwards of oral membrane to the transverse ridge, tc ; /./>, 

 lateral plate attached to the two transverse bars; r, mouth; ti/, mandibles; <?.;//, 

 oral membrane ; //, prelateral ; sp, spur for attachment of muscles. <( iy^. 



median and posterior margins. The exposed surface presents the 

 characteristic sculpture and the well known sensory groove. The 

 posterior margin is nearly smooth and sharply bevelled, ending 

 in an extremely thin edge nearly the whole length of which is 

 broken into irregular serrations. The lateral and central serra- 

 tions have more or less truncated points, the median ones are 

 more regular in shape, sharply pointed and directed diagonally 

 backward and inward toward the median line. The median mar- 

 gins of the mandibles are very thick and are provided with two 

 horizontal edges, Fig. 4, B. Anteriorly the innermost edge be- 

 comes nearly vertical, forming a sharp-edged, tooth-like process, 

 rounded in outline when seen from the side, Fig. 3. The plate 



