102 ON THE aENTJS CTENODUS. 



The teeth- are the parts of the fish Ctenodus that are most 

 frequently discovered, and they have been obtained in places 

 where no other remains of the endo- or exo-skeleton have been 

 observed ; they are most common in the true Coal Measures of 

 IN'orthumberland ; occasional teeth are disinterred from the coal 

 formations of South Yorkshire and Staffordshire ; a single tooth 

 has been obtained from the carboniferous limestone of Derby- 

 shire ; and there is asiugle specimen in the British Museum that 

 is believed to have been found in the Coal Measures of Carluke, 

 in Scotland ; if the latter be a fact, then Carluke is the outermost 

 limit of this fish's geographical range to the north, and Derby- 

 shire is known to be the southern boundary ; but even within this 

 confined area the strata containing the remains are very small in 

 extent ; for example, Northumberland is the most prolific in its 

 supply, yet nearly all the specimens are obtained from a pit at 

 Newsham, the remainder being found at Cramlington ; the same 

 thing is observed in Staffordshire. Besides the narrow range of 

 this fish, we can also judge that its habitat was in the shallow 

 brackish waters of estuaries, and the mixed waters of the sea 

 3iear the mouths of rivers ; for we find its remains fossilized in 

 the shales, in which are also imbedded numerous Cestracionfs 

 and Ganoids that certainly did not exist in fresh water, although 

 they frequently roamed into the deep seas ; such are Cladodtis, 

 Fsammodus, Falwonisctts, Rliizodus, &c. To this fact there 

 appears to Idc an exception. I refer to the tooth foimd in the 

 Derbyshire limestone, that seems to prove that Ctenodus was also 

 a deep-sea fish, but a little thought will show its improbability ; 

 only one tooth has been obtained from that stratum, notwith- 

 standing the extensive researches that have been made into it ; 

 the tooth has, therefore, been most probably carried out into the 

 deep sea by a strong under-current, or a solitary fish may have 

 strayed out and died from inability to exist in a foreign water, 

 leaving its remains to decay or become imbedded in the forming 

 limestone. That Ctenodus did not live in fresh water is clearly 

 proved by the fact that the shale containing these teeth has never 

 been observed, by me at least, to contain fossilized terrestrial or 

 fresh-water vegetation. So much for the classification, geo- 

 graphical range, and habitat of Ctenodus. We will now turn to 

 the fish itself, and in this paper I shall confine myself to the 

 teeth, describing the characters of the different species and illus- 

 trating them by drawings. In future papers I shall pourtray 

 their microscopical structure, draw attention to the characters of 

 the bones that enter into the formation of the mouth and the 

 mode of arrangement of the teeth, and finish by describing the 

 endo- and exo-skeleton. 



C. cristatus was the first species named by Agassiz, and was 

 founded upon a tooth at present in the Leeds Museum ; Mr. 



