CROCODILIA. 41 



it does not sink deeper than the line of the posterior border of the pterygoids ; and this 



modification is exaggerated in the Crocodilus Hastingsics (T. VI, fig. 3) in which the notch 



in question is merely the interval between two slender diverging processes from the 



middle of the back part of the pterygoids, 24. The posterior aperture of the nasal 



passages is wholly surrounded in the Crocodilus Hastingsics by the horizontal plate of 



the pterygoids, and has the same position and aspect as in the Alligators ; but its form 



is heart-shaped, with the apex directed backwards, and the antero-posterior diameter 



exceeding the transverse one. I have not met with this form of the posterior nostril 



in any other species of Crocodilian ; but it is repeated in two individuals of the Croc. 



Hastingsics, and may be regarded as a specific character. 



The ectopterygoid, 25, T. VI, fig. 3, T. II, fig. 2 (d, fig. 2, pi. iii, ' Ossemens 



Fossiles,' t. v, pt. ii) articulates with a larger proportion of the outer surface of the 



pterygoids (24) in the Crocodiles than in the Alligators : it agrees with the Crocodiles 



in the extent of this articulation in the Croc. Hastingsics. 



22—22 



The number of teeth in this species is 9Q _ 2Q — 84. 



In the upper jaw the fourth, ninth, and tenth are the largest ; and the fifteenth 

 and sixteenth exceed in size those immediately before and behind them. The alveolar 

 border of the jaw increases in depth to form the sockets requisite for firmly lodging 

 these larger teeth, and gives rise to the festooned outline of the jaw, which is found in 

 all Crocodiles and Alligators in proportion as the teeth are unequal in size. 



The lower jaw presents the same compound structure as that in the Crocodilia, 

 with the general form characteristic of that in the Alligators and in most of the true 

 Crocodiles : the symphysis, e. g. is as short as Crocodilus biporcatus and the Alligator 

 niger, in which it extends as far back as the interval between the fourth and fifth 

 socket. This is the relative position of the back end of the symphysis in a fine and 

 perfect under jaw of the Crocodilus Hastingsics in the collection of the Marchioness of 

 Hastings. In a portion of the under jaw of apparently the same species of Crocodile, 

 from the same locality, in the collection of Searles Wood, Esq., F. G. S., the symphysis 

 terminates opposite the interval between the third and fourth tooth. 



The chief distinction observable between the modern Crocodiles and Alligators in 

 the lower jaw is the greater relative size of the vacuity between the angular (30) and 

 surangular (29) pieces, and the greater relative depth of the ramus at that part, in the 

 Alligators. In these characters the lower jaw of the present species more resembles 

 that of the true Crocodiles ; although, as the vacuity in question is somewhat larger, 

 a slight affinity to the Alligator might be inferred from that circumstance. The 

 comparative figures of the hinder third of the mandibular ramus in T. XII, fig. 4, 5, 6, 

 will exemplify the difference in question, and the degree of proximity to the crocodilian 

 and alligatorial characters respectively. 



With regard to another character deducible from the relation of the backwardly- 

 produced angle of the jaw to the articular surface, the Crocodilus Hastingsics more 



6 



