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 Procellariide. (Vide Pl. Il. fig. 19, 
giving an enlarged view of the palate of Oceanites oceanicus.) 
Pagodroma resembles Cistrelata, 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 
premaxilla 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 banksit) 
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 
lamelle, reminding one much of the plates of a whale’s baleen. These lamelle 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 Pl. VI. fig. 4). 
They are best developed a little way in front of their posterior termination of the fringe ; 
here the lamellee 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 bill is in position, the more posterior and strongest of the lamelle 
completely occupy the sight 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 lamelle of 
the fringe—of the lower jaw, which in front it does not even reach. In the larger-billed 
Prion vittatus these lamella 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.! 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. ‘ 
