CRETACEOUS LIZARDS. 187 



and one fourth that of the former species. But the characters of immaturity are not 

 manifested by the cold-blooded animals in their osseous and dental systems as they 

 are in the warm-blooded and higher organised mammalia.* 



In all the teeth of the Mosasaurus gracilis in which the crown is broken, the 

 remains of the pulp-cavity are exposed in the centre of its base : but the immaturity 

 of the specimen is not demonstrated by this character ; for, in the largest sized teeth 

 of the Mosasaurus Hoffmanni, even in one with a completely developed fang, measuring 

 with the crown nearly five inches in length, I have found a pulp-cavity extending 

 from the base of the crown into the expanded fang, but becoming almost obliterated 

 at the base of the fang. The cast of the crown of a still larger tooth of a Mosasaurus 

 from the green-sand of New Jersey, U.S., also shows the remains of a pulp-cavity at 

 its base. This cavity becomes filled in the fossil specimens with the matrix, which 

 is usually chalk ; but sometimes the cavity, like the air-chambers of polythalamous 

 shells, is filled with silex. 



The number of teeth in each ramus of the lower jaw o^ 3Iosasaurus gracilis seems 

 not to have exceeded twelve. In Mosasaurus Maximiliani they are reckoned at eleven ;f 

 in Mosasaurus Hoffmanni at fourteen ; and in this species they are placed closer 

 together than in the Mas. gracilis, as may be seen by comparing figure 1 of PI. 2 

 with that of the lower jaw given by Camper in the ' Philosoi^hical Transactions ' for 

 1786, tab. xvi, which is copied by Faujas St. Fond, in pi. vi, of his ' Histoire de la 

 Montagne de St. Pierre.' j The posterior teeth are rather smaller than the others in 

 Mosasaurus gracilis. At the fore part of the jaw the implanted and anchylosed base 

 of the teeth extends through about half the vertical diameter of the jaw ; at the 

 posterior part of the series the fangs sink into one third or one fourth the depth of 

 the jaw. The canal, which, as in the crocodile, extends below and along the inner 

 side of the bases of the sockets and anchylosed fangs, is shown, filled by chalk, at 

 d, fig. 1. Traces of the vascular foramina along the outer side of the jaw are visible 

 in the right dentary piece, the outer side of which is exposed : the " splenial " 

 (" opercular," Cuvier,) element is shown at x, fig. 1, on the left ramus. 



In the portion of the left superior maxillary bone (PI, 2, fig. 1 a) all the teetli 

 are, unluckily, too much broken or abraded to give an idea of the precise form of 

 their crowns ; they are rather more compressed at their base tlian in Mosasaurus 

 Hoffmanni : the posterior ridge is much less developed, and the whole of the posterior 

 longitudinally concave border is more transversely convex than in Mosasaurus Hoffnumm 

 or 3Ios. Maximiliani. There is as little indication of the angular or polygonal 



* Dr. Goldfuss infers the maturity of his Mosasaurus Maxhniliaiii from the characters, of which the 

 inadequacy is exphiined above. "Die vollstiindige Verlinocherung alter Tlieile, so wie die hiiufige bemerk- 

 bare Aussfullung der Zahne beweisen, dass das Individuum seine vollstiindige Ausbildung und mit dieser 

 nur die halbe liinge des Mosasaurus Hoffmanni erreicht hatte." (Ijoc. cit., p. 177.) 



t Goldfuss, loc. cit. p. 178. % Cuvier, loc. cit. p. 320. 



