548' PROF. W. B. BENH^M AND MR, W. J. DUNBAR ON [May 15, 



being almost equal in length ; whereas in the present species the 

 nasal process is more than twice the length of the alveolar plate. 

 Again, the longer axis of this plate is, in R. glesne, vertical and 

 perpendicular to the nasal process, while in R. parkeri the longer 

 axis of the plate is almost horizontal and parallel to the nasal 

 process (PI. XXXVIII. fig. 1). 



The Maxilla, instead of being, as in a typical teleostean skull, a 

 narrow rod of bone, is broad and subquadrate, marked on its 

 outer surface by ridges — as in other dermal bones of Regalecus — 

 which rise from a point near the dorsal posterior border (fig. 1). 

 The maxilla overlaps the hinder part of the alveolar plate of the 

 premaxilla, and can be distinctly seen through the silvery 

 epidermis. On its inner side is a pronounced ridge, which is 

 continued beyond the posterior margin of the bone as a peg-like 

 process {mx.') lying alongside the nasal process of the prem.axilla 

 (PL XXXVIII. fig. 1 and PI. XXXIX. fig. 3). The antero- 

 posterior length is somewhat greater than the vertical height, 

 whereas in R. glesne the bone is long and narrow, and is at least 

 twice as high dorso-ventrally as it is wide : in fact its relation 

 to mouth is more like that commonly met with in Teleosteans. 



The lower jaw (PL XXXVIII. figs. 1 , 2) consists of the usual three 

 bones, the Dentaiy, the Articulare, and the Angulare, enclosing 

 Meckel's cartilage, which is distinctly visible through them. The 

 region above Meckel's cartilage may be termed the supra-meckelian, 

 and the part below that line the infra-meckelian region. In R. 

 glesne, Prof. Parker describes the supra-meckelian part of the lower 

 jaw as having " something the form of an equilateral triangle and 

 the infra-meckelian of a right-angled triangle with altitude about 

 one-fourth of its base, so that the whole jaw comes to be rather 

 higher than long." In the present species the height of the lower 

 jaw is veiy much greater than the length, and the proportions of 

 the two regions are different from R. glesne. The supra-meckelian 

 portion has the form of an isosceles right triangle with one limb 

 of the dentary as hypotenuse. The infra-meckelian portion is an 

 irregular four-sided figure whose height is one half its length ; it 

 is thus just twice as high proportionately as that of Regalecus 

 glesne (PL XXXVIII. fig. 2). 



Hhe Articulare («r.) is a thin plate of bone somewhat triangular 

 in form. The posterior side is vei-tical and extends upwards as 

 far as the peg of the maxilla. This posterior margin is much 

 thickened. The lower margin is also slightly thickened, and 

 extends horizontally below Meckel's cartilage, overlapping and 

 concealing the angulare externally. The thii'd side slopes down- 

 wards and forwards and meets the dentary along the edge. 



The Dentary {d.) is a V-shaped bone placed with the angle 

 forwards and bearing at the extremity one tooth which is not 

 present in R. glesne. The two limbs meet one another at an angle 

 of 90°, one being directed backwards and upwards to meet the 

 articulare above, the other passing below Meckel's cartilage to 

 meet the lower border of the articulare. 



