2:^0 MR. A. S. WOODWARD ON THE MANDIBULAR [Apr. 20, 



obtained from the Chalk of Kent, and is in an excellent state of 

 preservation. It agrees in all important respects with a less perfect 

 specimen in the same collection, which forms the type of Hybodus 

 dubrisiensis, Mackie ^ — this fossil having been placed with the 

 Hybodonts in the Museum series by Mr. William Davies, and 

 subsequently figured by the editor of t!ie ' Geologist ' under the 

 name just quoted. And it may be added that the teeth are undis- 

 tinguishable in general character from those of the typical species 

 of /Tyiot^MS of earlier date. The specimen (Plate XX.) exhibits the 

 pterygo-quadrate and Meckelian cartilages of each side.'those on the 

 right, however, being broken away for about the hinder third ; on the 

 left side, the two elements of the hyoid arch are well shown in their 

 natural position, and less complete remains of the corresponding 

 cartilages are also seen on the right. Teeth and shagreen granules 

 are abundant, and three well-calcified vertebrae ajipear at the back. 



The pteri/ffo- quadrate cartilage (figs. 1, 2, pq) measui'es 0'073 ni. 

 in length, and varies considerably in depth at different points. At 

 the anterior end it is comparatively low and somewhat folded 

 inwards above, but it soon begins to deepen by the rising of the 

 upper border, which rapidly ascends to form a pterygo-trabecidar 

 process (p) ; this is placed at about one third of the distance from 

 the fore to the hinder extremity. The process is almost pointed, 

 and posteriorly the upper contour at once falls again to some extent, 

 tliough soon re-ascending in the form of a gentle curve to a still 

 higher prominence (of), which exhibits in front a very distinct, 

 relatively broad articular facette. Tliis occurs at about the end of 

 the second third of the cartilage, and thus far the characters are 

 shown on both the left and right sides of the fossil ; but the 

 hindermoBt third is only preserved to the left. A little lieyond the 

 summit of the facette, ti.e upper border becomes thickened and 

 turned outwards, and its edge forms a regular gentle curve down to 

 the articulation of the low^er jaw. The inferior border of the car- 

 tilage is almost straight for its anterior two thirds, the dentigerous 

 portion, and then tliere follows a curved hollowing ; next is a minute 

 process, marking the commencement of the articular portion, whicii 

 shows two small hoUowings and a teniunal convex condyle. 



The MecA-elian cartilage, or lower jaw (ni/c), is preserved on both 

 bides of the fossil, but is only perfect on the left. It measures 

 0-0C85 m. in total length, being thus somewhat shorter tliau 

 the pterygo-quadrate. Tiie upper contour is almost straight from 

 end to end, only a slight hollowing being perceptible immediately 

 beyond the termination of the tooth-bearing portion ; and this is 

 succeeded by a short, wavy articular edge, fitting into the corre- 

 sponding irregularities at the hinder end of the pterygo-quadrate, 

 and finally presenting a distinct concavity for the reception of the 

 upper condyle. The cartilage is deejjest just beneath the end of the 

 dentigerous portion, from which point the lower border curves 

 upwards both in front and behind ; posteriorly the curve is at first 



' S. J. Mackie, " On a new Species of Hyhodus from the Lower- Cha]k," 

 ' The Geologist,' vol. vi. (18CS), pp. 241-24('), jjl. .\iii. 



