10 BULLETIN OF THE 



The upper jaw, quadrato-pterygoid {q-pg), is a broad, thin, twisted 

 blade, a trifle over five inches in length. Anteriorly it is spatulate, near 

 seven tenths of an inch in width, and is twisted so as to rest obliquely 

 under the skull, the lower edge being turned outward. Posteriorly it is 

 more than an inch in width, strongly convex on the inner side, deeply 

 concave on the outer, and at the articulation with the meckelian is 

 twisted half-way around so as to bring the side of the extremity in 

 contact with the latter. An inch and three quarters back from its front 

 end it bears a strong, compressed, palatal or trabecular process {tp). 

 This process is a little more than half an inch in height, a little less in 

 width, and is rounded on its upper edge, where it is attached by ligament 

 to the skull near the top of the orbital cavity. Its outer and inner faces 

 are convex ; the latter being received in a concave articular depression 

 in the skull. At the sides and beneath, this concavity has been enlarged 

 by ridges of cartilage. Half an inch from the hinder end the pterygo- 

 quadrate bears a small hyal process, which is overlaid by a similar one 

 on the hyomandibular. Two inches from the same end there is a larger 

 process, quadratic or otic {qp), formed by a short bend in the thin 

 upper edge. Some of the most prominent differences between Chlamy- 

 doselachus and the Xotidanidso are to be seen in the attachments and 

 articulations of this cartilage. 



The lower jaw, MeckeVs cartilage (mk), is a strong, broad, twisted 

 cartilage. It is broad posteriorly, and tapers gradually forward to near 

 the end, where it decreases in size rapidly aud presents but a small sur- 

 face to its fellow from the opposite side at the symphysis. It is twisted 

 in front to bring the sharp upper edge outward, where the cartilage 

 bends inward toward the middle of the snout. In the posterior two 

 thirds of the length the lower border is wide, with a sort of flange ; for- 

 ward the outer edge of this flange fades into the middle of the blade, 

 while the inner continues as the inner edge. Backward the lower jaw 

 is convex on the inner side, and deeply concave on the outer. Bending 

 outward at the end, the articulation of the pterygo-quadrate with this 

 cartilage has the appearance of taking place on the upper edge. 



The Ceratohyals {chy) are moderately slender, curved, club-shaped or 

 bilotate anteriorly, and tapering in the posterior two fifths of their 

 length, where applied aud attached by ligament to the meckelians. 

 Though the thick front lobe articulates with the side of the basihyal, 

 the outer and thinner lobe underlies the hinder angle of that cartilage. 

 The latter reaches back above the ceratohyal to articulate with the first 

 ceratobranchial. In the figure the lobe has been brought too far back, 

 and too near its fellow on the opposite side of the basihyal. 



