412 PLAGIAULAX. 



diagonally downwards and forwards, disappearing about the 

 middle of the crown-side, upon a smooth and discoidal sur- 

 face. The enamel below the four last grooves is inequal and 

 raised into a well-marked crenated step (PI. XXXIII. fig. 5), 

 which is exhibited on all the specimens. The interior surface 

 being adherent to the matrix, the characters of the inner side 

 of the last premolar are not shown by this specimen. But in 

 two of the other specimens the inner surface of all the pre- 

 molars is free and seen to be furrowed by diagonal grooves, 

 exactly like the outer, the principal difference being that the 

 inner side is more flattened, and the enamel smoother than 

 on the outer. The two sides, therefore, slope from the base 

 upwards to a sharp or thin edge, which is serrulated, agreeing 

 in every respect, except the inclination of the grooves, with 

 the corresponding tooth of Hypsiprymnus. The tooth is im- 

 planted by two distinct fangs. The penultimate premolar is 

 somewhat spathulate in outline, the lateral surface of the 

 crown is convex in the longitudinal direction, and slopes 

 inwards to the apex, which is diagonally grooved like the 

 last premolar, the grooves being fewer in number. It is 

 inserted by two inequal fangs, the posterior of which is 

 barely visible ; in size it corresponds with one fang division 

 of the last premolar. The antepenultimate or anterior pre- 

 molar is greatly reduced in all its dimensions, being hardly 

 one-fourth the size of the tooth immediately behind it ; in 

 form it exhibits more the ordinary appearance of an incisor. 

 In the other species, Plagiaulax minor (Plate XXXIV. 

 fig. 2), which is very considerably smaller, the incisor (a) pre- 

 sents a corresponding general form, but it is more elongated, 

 less robust, and is not so much curved upwards. A portion of 

 the point has been broken off in the specimen, and it is seen 

 by the impression (a') that the inner side near the apex was 

 hollowed out in a longitudinal depression. The premolars, 

 in number four, are higher in proportion to the depth of the 

 jaw than in the other species. The last one is similar in 

 form and grooving to the corresponding tooth in Plagiaulax 

 BecJclesii, but exhibits a slight difference in the inequality of 

 the enamel-surface below the basal terminations of the 

 grooves. In front of it there are two spathulate premolars, 

 i.e. the antepenultimate and penultimate, both diagonally 

 grooved near the apex ; and at the base of the antepenulti- 

 mate, but pressed somewhat inwards, there is a very minute 

 anterior or first premolar. The basal enamel- surface bulges 

 out over the fangs in these teeth in a rounded angle which 

 points downwards. Regarded as a series, they decrease in 

 size very rapidly from the last to the foremost. The sharp 

 edge of the crowns of the three anterior teeth slopes down 



