104 PROCEEDINGS OF THE ACADEMY OP [1883. 



series succeed each other in columns of from five to eight teeth 

 each, following an arc of a circle. The superior arc is convex 

 externally ; the inferior arc is convex internally, or towards the 

 position of the tongue. It results that the opposed grinding sur- 

 faces of the two dental series are vertical. The cementum-plate of 

 the tooth is, in both sets, on the convex side of the tooth, hence 

 external and inferior in the superior teeth, and internal and supe- 

 rior in the inferior teeth. The teeth replace each other differently 

 in the two jaws, or rather the replacement of the teeth does not 

 partake of the general reversal of relations which the opposite series 

 present in all other respects. The successional teeth rise in both 

 jaws on the inner sides of the older teeth. From this it follows, 

 that in'the superior series the replacement is on the non-functional 

 side of the tooth, or from the side which does not bear the cementum- 

 plate. In the lower jaw, the successional teeth follow on the side 

 that bears the cementum-plate, so that one tooth must be worn 

 away before the apex of its successor can come into use. The 

 arrangement of the superior series permits the successional to 

 overlap the functional tooth far beyond the base of the enamel- 

 plate, which in point of fact they do in the Diclonius mirabilis, 

 though not to the same extent as in the Cionodon arctatus. The 

 superior teeth are smaller and narrower in form than the inferior, 

 and both have a keel on the median line of their cementum-face. 

 There are no teeth on the anterior parts of the surangular bone 

 nor on the dentary or premaxillary bones. The extremity of the 

 muzzle is a flattened spatulate beak. 



Dermal or corneous structures have left distinct traces in the 

 soft matrix about the end of the beak-like muzzle. Laminse of 

 brown remnants of organic structures Avere exposed in removing 

 the matrix. One of these extends as a broad vertical band round 

 the sides, indicating a vertical rim to the lower jaw, like that 

 which surrounds some tea trays, and which probably represents the 

 tomia of the horny sheath of a bird's beak. At the front of the 

 muzzle its face is sharply undulate, presenting the appearance of 

 vertical columns with tooth-like apices. Corresponding tooth- 

 like processes, of much smaller size, alternate with them from 

 the upper jaw. These probably are the remains of a serration of 

 the extremital part of the horny tomia, such as exist on the lateral 

 portions in the lamellirostral birds. 



Systematic liesulls. — The structure of the skull of this species 

 adds some confirmation to the hypothesis of the avian affinities 



