AKD AFFIXITIES OF P0TA3I0GALE. 7 



second incisor is separated from the first by a nai'row space which receives the second 

 incisor of the lower jaw when the mouth is closed; it is triangular, compressed, with a 

 sharp anterior and a sharp posterior edge — the anterior edge being convex, and the 

 posterior slightly concave. The third incisor is of the same form as the second, but a 

 little smaller. The incisors are each implanted by a single fang. 



Since in the view here adopted the canine is supposed to be absent, the first pre- 

 molar follows immediately on the thiid incisor, with an interval so slight as to have no 

 claim to be regarded as a distinct diastema ; it is inserted by two fangs ; its crown is 

 slightly larger than that of the thii'd incisor, but otherwise it resembles it. The second 

 premolar is also implanted by two fangs, and is otherwise similar to the first. The third 

 has the form of a triangular pyramid, with a small cusp developed from the posterior 

 internal basal angle, and another from the posterior external ; it is implanted by three 

 fangs. 



The first, second, and third true molars are similar to one another : they are trian- 

 gular in horizontal section, with the apex of the triangle situated internally; the 

 greatest antero-posterior diameter of the crown is to its transverse diameter as 2:3; 

 the internal- angle of the crown presents a single cusp ; the centre, two ; and the 

 external side projects downwards as a tuberculate ridge ; they are each implanted by 

 three fangs. 



In the lower jaw (PI. II. & fig. 8, p. 11) the incisors present, as in the upper, the 

 usual single-fanged insertion. The first is very small, chisel-shaped, and with its crown 

 converging to that of its fellow. The second incisor is high, conical, curved, with the 

 concavity of the curve looking backwards, and presenting from its base to its apex two 

 surfaces separated by a sharp ridge ; it is sharp-pointed, and resembles a canine ; it is the 

 most projecting tooth in the jaw. The third incisor is small, irregularly conical, convex 

 anteriorly, concave posteriorly ; it is the smallest of the teeth, except the fii'st incisor. 



The first premolar is triangular, compressed, with a sharp convex anterior edge and a 

 sharp concave posterior edge ; it has but a single fang. The second premolar is trian- 

 gular, compressed, with sharp anterior and posterior edges ; it is implanted by two 

 fangs ; its crown is a little lower than that of the first, but it otherwise resembles it. 

 The third premolar is a little larger than the first, triangular, compressed, with sharp 

 anterior and posterior edges ; the anterior and posterior basal angles have each a small 

 tubercle ; it is implanted by two fangs. 



The first, second, and third true molars are prismatic, and equal in height to the 

 second premolar ; the crown is furnished with three cusps in front and a single one on 

 a lower level behind. They are each implanted by two fangs. 



A very striking aspect is given to the dental series by the form of the cro^ras of the 

 second, third, fourth, and fifth teeth of the upper jaw, which are all triangular, much 

 compressed, with sharp anterior and posterior edges, thus ^dvidly reminding us of the 

 teeth of certain sharks. In this respect they resemble the premolar teeth of the river- 



