ON DIPTERUS AND CTENODUS. • [ 397 



Carboniferous waters : it must have been quite able to hold its 

 own against Loxomma, or even against the moro powerful An- 

 thracosaurus. 



Notwithstanding the recent discovery of this large and for- 

 midable fish, we are in possession of more information respect- 

 ing it than has been attained in regard to many species that have 

 been acknowledged for years. The characters of the dentition 

 are perfectly determined : the mandible and praemaxilla have 

 been obtained in a good state of preservation, with the teeth at- 

 tached. The gill and jugular plates, too, have occurred in most 

 excellent condition, as well as several other bones, including 

 some that apparently belong to the thoracic girdle. The body- 

 scales have likewise been found associated with the bones. 



We have also good reason to conclude that the genus Arch- 

 ichthys occurs not only in other coal-fields, but likewise consi- 

 derably lower in the Carboniferous series. 



EXPLANATION OF PLATE XII. 



View of the inner surface of a portion of a mandibular ramus of Anthraco- 

 saurus Russetti, a little reduced in size : a, alveolar border ; b, infe- 

 rior margin; c, inner or splenial plate; d, outer plate or dentary 

 bone ; e, depression in alveolar border ; /, elevated straight portion 

 of ditto ; g, impression of first tooth of the series ; h, remains of the 

 last ditto. 



XVII. — A few Remarks on Dipterus and Ctenodus, and on their 

 Relationship to Ceratodus Forsteri, Krefft. By Albany Han- 

 cock, F.L.S., and Thomas Atthey. (Plates XIII., XIV.) 



In our paper on Ctenodus, published in a previous volume of 

 these Transactions,* while recognizing the close connexion be- 

 tween this genus and Dipterus, we deemed it prudent to keep 

 the two forms asunder, for certain reasons therein expressed ■ 

 and the time that has elapsed since then has only tended to 

 confirm us in this opinion. Among other characters that in- 

 fluenced us, stress was laid on the differences in the scales in the 



* See Natural History Transactions of Northumberland and Durham, Vol. III., p. 04. 



