REMAINS OF EEPTILES AND FISHES. 91 



be satisfied of this, it is only necessary to examine a longitudinal 

 section of the tooth of Megalichthys, or any other tooth with a 

 plicated base. 



The variety G. undatus (pi. 7, fig. 7) is most assuredly the 

 tooth of Strepsoclus sauroicles, Huxley : the double bend of the 

 apex and general proportions of the crown put this beyond doubt. 



A fragment of a maxillary bone of RJiizodopsis has, it is im- 

 possible to doubt, served for the establishment of the so-called 

 Characodus (pi. 13). Here there is not one tooth left, they are 

 all broken away; but the form of the fragment itself, tapering 

 at one extremity and suddenly expanding at the other, as like- 

 wise the columnar structure of the bone for the support of the 

 teeth, prove this to be an imperfect maxillary of Rhizodopsis 

 sauroides. These peculiar pillars of bone supporting the teeth 

 are very characteristic of the jaw-bones of this fish; but in the 

 maxilla they are most developed. Some of our specimens (Plate 

 I., fig. 5) are precisely similar to that figured as Characodus, the 

 teeth having been all broken away, with the exception of three 

 or four. The display of this curious structure depends much 

 on the plane of the sections ; it is possible to cut it nearly all 

 away, leaving merely the external layer of bone on one side ; 

 and it is never developed to the same extent in the prsemaxUla 

 and mandible. 



The prasmaxilla is the basis of the genus Gasirodus (pis. 14, 

 15) the supposed Batrachian, as is evinced by the shape of the 

 fragment, the size, form, character, and disposition of the teeth ; 

 nor is there any important difi'erence in the minute structure of 

 the teeth in this so-called genus. According to Prof. Owen's 

 measurements, the dentinal tubules in Dittodus parallelus have a 

 diameter of y-oi-ro of an inch, in Characodus t^-o "o oi an inch, 

 and in Gastrodus tt^o o o ; while in Rhizodopsis we have ascer- 

 tained that they are likewise about xo-oo-o of an inch in diameter. 

 The teeth of the so-called Gastrodus are certainly represented to 

 be without enamel ; but we have seen that it is frequently absent 

 in Rhizodopsis ; and many of the teeth, as exhibited in the figure, 

 are cut diagonally short, so that their form and proportions are 

 destroyed. The appearance thus presented is very common in 



