382 CRETACEOUS REPTILES. 
the general fang to the bony walls of the socket, which rise in a pyramidal form 
from the alveolar border of the jaw; manifest the peculiar generic characters 
of the great acrodont marine lizard, Mosasaurus. The maturity of the individual 
from which the present specimen (Pl. XX XVII. fig. 1) has been derived, cannot 
be inferred from the solidification and complete development of the anchylosed 
fangs of the teeth in a class of animals in which those organs are repeatedly shed 
and renewed: the worn-out teeth, in course of displacement, of the young 
Crocodile, with their alveoli, present in miniature all the senile characters of the 
corresponding teeth of the mature and aged animal. If, however, the specimen 
of Mosasaur in question should be adult, it would derive a well-marked specific 
character from its diminutive size as compared with the Mosasaurus Hofmanni 
or Mos. Mazimiliani; being only one-half the size of the latter, and one-fourth 
that of the former species. But the characters of immaturity are not mani- 
fested by the cold-blooded animals in their osseous and dental systems as they 
are in the warm-blooded and higher organized 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 imma- 
turity of the specimen is not demonstrated by this character ; for, in the largest- 
sized teeth of the Mosasaurus Hofmanni, even in one with a completely de- 
veloped 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 greensand 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 of Mosasaurus gracilis 
seems not to have exceeded twelve. In Mosasaurus Maaimiliani they are 
reckoned at eleven} ; in Mosasaurus Hofmanni at fourteen{. 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 
* Dr. Goldfuss infers the maturity of his Mosasaurus Maximiliani from the characters, of which 
the inadequacy is explained above. “ Die vollstiindige Verknocherung aller Theile, so wie die haufige 
bemerkbare Aussfullung der Zihne beweisen, dass das Individuum seine vollstandige Ausbildung 
und mit dieser nur die halbe linge des Mosasaurus Hofmanni erreicht hatte.” (J. c. p. 177.) 
+ Goldfuss, Joe. cit. p. 178. { Cuvier, doc. cit. p. 320. 
