200 NOTE ON AN UNDESCRIBED FOSSIL FISH. 



large laniary tooth, exhibiting the same minute characteristic 

 striation, but do not seem to be folded at the base. The first 

 of these is about a quarter of an inch behind the large tooth ; 

 the next two are about the same distance apart from each other 

 and from the first tooth ; the fourth, fifth, and sixth are divided 

 from these and from each other by a space of five-eighths of an 

 inch ; the seventh is a little more than one-eighth of an inch 

 from the sixth, and a quarter of an inch from the eighth, which 

 is an eighth of an inch from the ninth, and this the last is an 

 inch and a quarter from the broken extremity of the mandible. 



The whole surface of the dentary bone is covered with small 

 rough tubercles, which have a tendency to run in lines, produc- 

 ing vermicular grooves. This peculiar character of bone-surface 

 at once associates our mandibular fragment with the remains al- 

 ready referred to, and supposed to be those of Rhizodus, and 

 for a description of which we must content ourselves, on the 

 present occasion, with referring to our paper " On Reptiles and 

 Fishes from the Shales of the Northumberland Coal-Field" (Ann. 

 Nat. Hist., Ser. 4, Vol. I., p. 346). But we may remark that 

 among these remains are many well-marked fragments and se- 

 veral perfect crescentic gill-plates or opercula, the largest being 

 six inches in length ; but one recently acquired is seven inches 

 long ; and a broken specimen in our possession could not have 

 measured much under eight inches when perfect. There are 

 also described along with these remains two or three jugular 

 plates six inches long ; and these are associated with a number 

 of the body-scales, three inches in diameter, usually supposed 

 to be those of Rhizodus. 



Here, then, we have the crescentic opercula usually attributed 

 to Rhiwdus, and jugular plates, with many other bones, all of 

 which have the surface-ornament similar to that assigned to 

 that fossil, and associated with the body -scales described as 

 belonging to it — occurring in a locality where the unmistakable 

 tooth of the large Rhizodus has never yet been found. But in 

 this locality another large tooth occurs, with peculiar characters, 

 and has now been found attached to a jaw the surface -ornament 

 of which perfectly accords with that of the above-mentioned 



