134 



WEALDEN AND PURBECK FOSSIL FISHES. 



ossified supraoccipital, bearing a vertical median crest on its posterior face; and 

 on either side of this there are remains of an equally well-ossified epiotic. These 

 bones are exposed as a narrow rim at the posterior border of the cranial roof. 

 As in P. Isevis, each parietal bone is longer than wide, and the squamosal is 

 relatively wide, though not much longer than the parietal. The large frontal 

 bones, as shown in the type specimen and in Mr. Hooley's fish (PI. XXV, fig. 4), 

 are narrowed between the orbits; but, as also shown in Mr. Hooley's specimens, 

 they are much expanded in the postorbital region and overlap the well-ossified 

 postfrontals to an undetermined extent. The parietals, squamosals and frontals 

 are marked only by fine radiating ridges and an occasional trace of the slime-canal, 



Kill 



Fig. 40. — Pachythrissops vectensis, A. S. Woodward; type skull, right lateral view, one-half nat. size. — 

 Wealden ; Isle of Wight. British Museum, no 12013. ag., articulo-angular ; </., dentary; enpt., 

 entopterygoid ; </., gill-rakers; Inn., hyomandibular; mjd., metapterygoid ; pmx., premaxilla; qu., 

 quadrate: so., portion of hinder cheek-plate. 



but along the middle of the cranial roof there is a well-marked depression, which 

 is widest and deepest between the hinder part of the orbits. The type specimen 

 proves that the ethmoid region is comparatively small. Fragments of very thin 

 cheek-plates occur in the type specimen (Text-fig. 40, so.) and in the, original of 

 PI. XXV, fig. 4; and a single broad series is seen to cover the postorbital region 

 of the cheek in PI. XXIV, fig. 6, so. These plates are nearly smooth, but are 

 marked with slight radiating ridges or finibriations. They are also traversed by 

 the slime-canal near the orbital border. The mandibular suspensorium curves 

 forwards so that the articulation for the mandible is beneath the hinder part of the 

 orbit. The hyomandibular (PI. XXV, fig. 5) is much expanded at the upper end, 

 with an apparently double-headed articulation; and, as in other fishes in which 



