Fossil Fis/ifroin the Xcws/tam ('uul-shale. 2(M 



sures an inch in length ; the base is broad, being quite five- 

 eightlis of an inch wide ; and the n))pcr, broken cxtreniitj is 

 three-eigliths of an incli across. When ])crfcct, this tooth 

 could not be less than an inch and hvc-cighths in length, as is 

 proved by comparing it witla a perfect tooth of the same size 

 at the base. The Ijase is deeply folded, the folds being rounded 

 and covered with minute, sharp, raised striaj, which pass up- 

 wards and die gradually out as they approach the In-oken 

 extremity. 



Along the alveolar border there are nine small teeth, three- 

 eighths of an inch long ; they have much the character of the 

 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 

 ninth, which is an inch and a quarter from the broken extre- 

 mity of the mandible. 



The whole surface of the dentary bone is covered with small 

 rough tuber^ which have a tendency to run in lines, pro- 

 ducing vermicular grooves. This peculiar character of bone- 

 surface at once associates our mandibular fragment with the 

 remains already refen-ed to, and supposed to be those of llhi- 

 zodus, and for a description of which we must content our- 

 selves, on the present occasion, with referring to our paper 

 " On Reptiles and Fishes from the Shales of the Northumber- 

 land 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 several perfect crescentic gill-plates or 

 opercula, the largest being six inches in length ; but one re- 

 cently 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 oi Rhizodus. 



Here, then, we have the crescentic opercula usually attri- 

 buted to li/nzoduSf and jugular plates, with many other bones, 

 all havinff the surface-ornament similar to that assis:ned to 

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

 belonging to it — all occurring in a locality where the unmis- 

 takable tooth of the large Rhizodus has never yet been found. 

 And in this locality another laroe tooth occurs, with peculiar 



18* 



