LEPTOTRACHELUS. 71 



of being a tube. This element is also ornamented with a few fine, longitudinal 

 ridges which terminate just behind the anterior expansion. 



The orbit is relatively large, its diameter equalling about one quarter of the 

 total length of the skull. No cheek-plates have been observed; but in some 

 specimens a piece of a smooth, convex, bony plate is seen (e. </., fig. 2, ,6'.), and this 

 may represent part of an ossified sclerotic. 



The mandibular suspensorium is vertical, so that the quadrate articulation is 

 directly beneath the occiput. As shown in fig. 4, the hyomandibular (km.) and the 

 triangular metapterygoid (mpt.), also perhaps the quadrate, are very thin plates. 

 The ectopterygoid (fig. 1 b, ecpt.) is relatively small, not forming more than a 

 third of the palato-pterygoid arcade. It is expanded behind into a thin triangular 

 lamina in a vertical plane, while its anterior portion is a comparatively stout bar, 

 tapering to a point in front where it rests in a groove on the upper face of the 

 palatine. Its anterior half alone bears teeth, which are very small, slender-conical, 

 and recurved, arranged in a close series or perhaps clustered. The palatine (figs, 

 la, 11), 2, 5, pi.) is large and stout and always conspicuous in the fossils. It is a 

 lenticular plate of bone, pointed at each end, and its maximum width seems to have 

 been contained about seven times in its total length. It must have been originally 

 disposed in an almost horizontal plane, perhaps a little inclined outwards and 

 downwards. Its upper face is nearly flat and smooth, only impressed at the hinder 

 end with the groove for the ectopterygoid. Its inferior face is completely covered 

 with a dense cluster of teeth, which are partly seen in the broken specimens repre- 

 sented in figs. 5, C. These teeth are slender, smooth, recurved cones, enamelled 

 only at the tip, and with so large a pulp-cavity that they are readily broken and 

 display their hollowness. When they are removed, their bases of attachment are 

 shown (as in fig. 6) to have been in very shallow sockets. The maxilla is unknown. 

 The premaxilla (figs. 2, 4, pmx.) is a long and slender, thin lamina of bone, meeting 

 its fellow of the opposite side in an extended symphysis anterior to the cranial 

 rostrum, and tapering in front to a sharp point. It is smooth, but marked by one 

 or two longitudinal ridges. Its straight oral margin bears a single close and 

 regular scries of minute conical teeth. The mandible is also long and slender, and 

 the bluntly-pointed, symphysial end of the dentary (fig. 4, d.) is not so far forwards 

 as the anterior end of the premaxillary rostrum. The upper jaw thus projects 

 beyond the lower jaw. The anterior part of the dentary at least is ornamented 

 with a few longitudinal ridges, and its oral margin bears a series of teeth like 

 those of the premaxilla. Some specimens also suggest that there may have been 

 a cluster of small conical teeth on the inner face of the mandible. 



The opercular and branchiostegal apparatus are almost unknown ; but one 

 specimen in the Willett Collection (no. 113), from the Upper Chalk of Brighton, 

 seems to show a normal suboperculum, which is quite smooth and more than twice 

 as broad as deep. 



