ICHTHYOPTERYGIA. 177 



folding of the walls of the conical teeth (fig. 1 1 1 F) paralleled 

 only by that observed in many Labyrinthodonts ; while their 

 short, biconcave vertebral centra are best compared with those 

 of such Labyrinthodonts as Mastodon saur us. 



The rostrum of the Ichthyopterygian skull (fig. Ill A D) is 

 formed by the enormously enlarged premaxillae (pmx.) and the 

 equally extensive mandibular syrnphysis. The external nares 

 (new.) thus remain close to the orbit, while the only note- 

 worthy disproportion in the other cranial bones is observed 

 in the diminishing frontals (fr.) and in the extending nasals 

 (int.). There is a very large pineal foramen (pin.) at the junc- 

 tion of the parietals and frontals. The supratemporal vacuities 

 are also large; and the sutures between all the component 

 elements of the temporal arcade remain distinct. There is a 

 conspicuous foramen between the quadrate (qu.) and the over- 

 lapping quadrato-jugal plate (q.j.). The otic bones are well- 

 ossified, and the pro-otic and opisthotic (op.o.) remain separate. 

 All the external bones are unornamented. The large eye is 

 protected by a ring of well-developed sclerotic plates (scl.). 

 The conical teeth forming a single series on the margin of the 

 jaws are placed in a groove only exceptionally sub-divided into 

 sockets ; and there are no teeth on the palate. The posterior 

 nares (pt.nar.) always occupy their primitive position on either 

 side of the vomers (v), and are never covered by secondarily- 

 developed palatine plates ; the relatively large pterygoids (pt.) 

 meet the vomers in front, abut against the quadrates (qu.) arid 

 the basipterygoid processes of the basisphenoid (b.s.) behind, 

 and are separated for the greater part of their length by a large 

 interpterygoid vacuity (i.pt.), along the middle of which the 

 well-developed parasphenoid splint (pas.) is conspicuous. The 

 transverse bone (ectopterygoid) has not been observed, though 

 there are indications of its having been articulated with part of 

 the hinder border of the maxilla (at x). There is a well- 

 developed " columella " (epipterygoid) rising to the prefrontal. 

 All the precaudal vertebrae (fig. Ill H) are essentially similar 

 in character, each centrum bearing two pairs of tubercles for the 

 support of the double-headed ribs. The atlas and axis are alone 

 peculiar. They (fig. Ill G) are almost invariably fused together 

 w. 12 



