Holt and Calderwood — Report on the Rarer Fishes. 467 



But although the relative length of the snout does not appear to be much 

 affected by the growth of the fish, our series shows a gradual transition in the 

 profile of the same organ, and of other parts of the head related thereto. Before 

 discussing this it is necessary to refer briefly to the general appearance of this 

 region. A glance at the figure shows that the strong infra-orbital ridge is 

 continuous with another ridge extending from the anterior extremity of the nasal 

 bones to the apex of the snout, and thus somewhat sharply dividing the pre-orbital 

 region into a dorsal and ventral area. It may be convenient to term this last the 

 "rostral" ridge; and on examining the head from above it is seen that the 

 rostral ridges meet at the apex of the snout in such a manner as to form practi- 

 cally a right angle, while each ridge makes a distinctly obtuse angle with the 

 anterior part of the infra-orbital ridge of its own side. The direction of the ridges 

 is here considered as straight, though as a matter of fact the infra-orbital ridge is 

 somewhat convex, and the rostral ridge is, in preserved specimens at any rate, 

 frequently concave. As such it is shown in Giinther's excellent figure {op, cit, 

 pi. xxxii., fig. c); but it is evident from our series that the ridge may run in 

 a straight, or even in a slightly convex, direction between the tips of the nasal and 

 ethmoid bones ; and we are strongly inclined to believe that the concavity, when 

 it exists, is due to the collapsing of the underlying muciferous cavities by the 

 action of the preserving fluid. 



Returning to the lateral point of view, the figure (which represents the 

 specimen here designated as 4) shows that the obliquely upward direction of the 

 infra-orbital ridge is continued by the dorsal ridge, and consequently the tip of 

 the snout is above the level of the tip of the nasal bones. Such is also the case in 

 the figure of Grtlnther's type specimen, which is about the same size as A, and it 

 is also the case, and to a rather greater extent, in X. However, as we turn to the 

 smaller examples, we find that in each the level of the snout is slightly more 

 depressed, the rostral ridge assuming a direction more nearly parallel to that of 

 the long axis of the head and body, until, in Z>, the tip of the snout is actually 

 rather lower than the end of the nasal bones. Very small specimens of 

 M. cequalis therefore exhibit, in the profile of the snout, a closer resemblance to 

 M. sclerorhynchus * than to adults of their own species, though agreeing with the 

 latter in the length of the organ. The mouth maintaining much the same relative 

 distance from the tip of the snout throughout the series, and at the same time being 

 restricted to about the same horizontal plane, it follows that the anterior profile 

 (ventral to the snout) becomes gradually more oblique as the size diminishes and 

 the mouth is displaced further backwards. Thus, while in -X" and A the angle of the 

 jaw barely reaches the level of the centre of the eye, in D it extends nearly to the 



* Cf. Giinther, op. cit., pi. xxxii., whereia adults of both species are figured. 



3 U 2 



