18 THE VOYAGE OF H.M.S. CHALLENGER. 



The prenarial ridge may be slightly toothed or nearly smooth : it always ends, however, 

 at the commencement of the median fissure, in a slightly raised prominence, divided into 

 two lateral parts, in a way not seen amongst the Procellariidae. (Vide Yl. II. fig. 19, 

 giving an enlarged view of the palate of Oceanites oceanicus.) 



Pagodroma resembles CEstrelata, but all the spines have become much smaller and 

 weaker, and this is still more the case in Daption, where they have almost entirely 

 disappeared save round the posterior nares. The line of the interior margins of the 

 premaxillaa and of the palatines is marked by a distinct raised ridge, and the edges of 

 the upper mandible, from the angle of the mouth as far forwards as the dertrum, are 

 marked by a series of slight, closely-set, raised ridges, oblique forwards and outwards. 

 It is by a great development of these that the peculiar fringed bill of the genus Prion, 

 reminding one of that of a duck, is produced. In Prion (t.c, fig. 23, Prion banksii) 

 the palate is almost smooth throughout, with the exception of a distinct prenarial 

 ridge, and some indications of the palatine series of spines posteriorly (not repre- 

 sented in the figure) : the median fissure and narial opening are however, as usual, 

 bounded by small spines. From a point corresponding to the angle of the mouth 

 forwards to a little behind where the dertrum forms the cutting edge of the bill, 

 the margins of the mouth are bounded by a well- developed fringe of closely-set 

 lamellae, reminding one much of the plates of a whale's baleen. These lamellae are 

 developed from the mucous membrane of the mouth, and are probably entirely epidermic 

 in origin ; in the cleaned skull there is no trace of their presence (vide PI. VI. fig. 4). 

 They are best developed a little way in front of their posterior termination of the fringe ; 

 here the lamellae are nearly vertical thin plates, set on at right angles to the axis of the 

 beak, but curved both forwards and outwards. Anteriorly they become more oblique 

 forwards, and much shorter. Outside of them the cutting edge of the beak is produced 

 downwards for a little way, so that a groove is formed between the beak and the 

 pectinated fringe. 



When the lower bdl is in position, the more posterior and strongest of the lamellaa 

 completely occupy the slight space left between the cutting edge of the two jaws, lying 

 with their free ends curved outwards in a slight groove outside the lower mandible formed 

 by the reflection from it of the feather-covered skin. Anteriorly this groove disappears, 

 and the fringe simply lies against the outer surface — which is quite smooth, and not, like 

 that of the duck or flamingo, correspondingly grooved for the reception of the lamellae of 

 the fringe — of the lower jaw, which in front it does not even reach. In the larger-billed 

 Prion vittatus these lamellae are even more developed, whilst in the smaller-billed Prion 

 desolatus they are less so : Prion banksi is so completely intermediate in this respect 

 that I see no reason for the adoption of Dr. Coues' genus Pseudoprion. 1 The only other 



1 Proc. Ac. Nat. Sci. Phil., 1866, p. 164, where that writer has also described the structure of these fringes at 

 length. 



