GARMAN : THE CHIMAEROIDS. 255 



from the nourishing tissues and a continuous grinding away on the side toward 

 the moutli cavity. 



The mouth of Rhinochimaera is narrower and more pointed than that of its 

 fellows, probahly in these respects approaching that of Rhynchodus, or of 

 Rhamphodus, consequently its teeth are narrower and more elongate, Plate 5, 

 Figures 1 and 2. Altogether the mouth resembles in a measure the beak of a 

 bird of prey ; the teeth pass one another like the edges of a pair of shears and 

 in front the vomerines are turned downward in a sharp hook. As the teeth 

 are used entirely for cutting and holding and not for crushing, the stress comes 

 on the sharp edges. The unassisted eye may hardly detect the existence of 

 tritors, but with a lens, where the edges have been somewhat worn away, a 

 series of the extremities of minute calcigerous tubes or pores is to be recog- 

 nized. The dental plates are thin ; in appearance tliey recall the horny fin 

 rays, though they are not fibrous and are much harder and more brittle. The 

 vomerines are small, convex outwardly, concave inwardly, in contact forward, 

 hooked downward in front of the lower jaws, and feebly notched on the lateral 

 cutting edge by contact with the mandibulars. The palatines are not in con- 

 tact on the median line of the mouth ; eaeh of the pair is long and narrow, 

 concave on the lower surface, blunt on the inner angle, slender and acute pos- 

 teriorly, straight on the cutting edge except at the forward extremity where it 

 curves upward, and but little bent upward on the inner edge. The man- 

 dibulars are longer, more slender, and more pointed than the palatines ; they are 

 concave on their upper surfaces, rounded instead of angled inwardly, slightly 

 in contact at the symphysis, very little bent downward at the. inner edges, and 

 straiirht on the cutting edires except when curvinsr down and inward below the 

 vomerines. The only tritoral areas on these teeth are on the cutting edges. 

 ProbaV)ly the teeth of Rhinochimaera do not vary greatly from the type pos- 

 sessed by the ancestral C'himaeroid, and no doubt the changes undergone in the 

 teeth from very young to adult stages are comparatively slight. The indicated 

 food of this C'himaeroid is crustacean and other life, of considerable depths of 

 the ocean, in wliich the skeletons have no great degree of hardness. 



Harriotta, in most respects the nearest ally of Rhinochimaera, differs radi- 

 cally in regard to the teeth, Plate 5, Figures 3, 4, G-9. The dental plates are 

 similar in shape and alike in number, but the tritors, even though they owe 

 their existence to the common causes, stress and impact without perceptible 

 differences in regard to exertion or reception, differ in arrangement from those 

 of any other known Chimaeroid either fossil or recent. The mouth being 

 wider in this genus than in Rhinochimaera and the function depending on the 

 side of the tooth, rather than on the edge, the teeth are broader and much 

 less sharpened at their extremities. The vomerines are of moderate size, 

 somewhat broad, convex outward, concave inward, slightly hooked down in 

 front of the mandibulars, and bear a marginal series of small tritors about 

 nine in number. They are in contact forward, and rather widely separated 

 backward on the median line. The palatines are broad, broadly rounded in 

 front and at the inner angle, more or less sharp posteriorly, and bear more or 



