NORTH STAFFORDSHIRE COAL FOSSILS. 245 



arranged tubercles." This arrangement is, however, subject 

 to variation. In some of our specimens the tubercles cover 

 only the ridges in the outer half of the palate : in all of 

 them the tubercles are largest on the outer margin. (See 

 plate, fig. 2.) The mandibular teeth (see plate, fig, 1) are 

 narrower than the palatal. Our largest specimen measures 

 three inches in length, and an inch and a half in breadth, 

 The upper surface of this tooth is convex and covered with 

 eighteen transverse ridges. The summit of the ridges is 

 studded " from end to end " with tubercles : those on the 

 outer border being conical, the rest becoming more elongated 

 posteriorly. Like the palatal teeth, the number and arrange- 

 ment of the tubercles is not constant. In some specimens 

 there are only five tubercles on the anterior half of the 

 tooth. At present we are unable to determine whether 

 these variations are of specific importance. In addition to 

 a large series of detached bones of Ctenodi which have 

 been collected in various parts of the coalfield, we have 

 one or two specimens showing a large portion of the skull. 

 One of these displays the bones belonging to the anterior 

 part of the head lying in their natural position, and the 

 various bones are distinguished by well-defined sutures. 

 A mandibular tooth two and a half inches long and one 

 inch broad is lying apparently in situ. This tooth has 

 fourteen transverse ridges studded anteriorly with tubercles. 

 A second specimen shows several of the head bones in- 

 differently preserved. A mandibular tooth of the same 

 size and number of ridges as mentioned above, together 

 with the impression of a palatal tooth, is seen lying on 

 the same slab. Several elongated bones, which are no 

 doubt sphenoid bones, with a wide expansion near the 

 anterior extremity, have occurred. Two or three large, 

 nearly circular plates, which are probably opercular plates 

 of Ctenodi, slightly convex on the upper side, measuring six 



