1894,] SAIMONOID PISHES OF THE ENGLISH CHALK. 657 



British Museum exhibit both the head and trunk with fins, and 

 these form the basis of the following detailed description. 



The hinder half of the cranial roof, the facial and opercular 

 bones, and the upper branchiostegal rays are ornamented with 

 rugae, mostly radiating. The cranial roof is flattened, with a faint 

 tendency to a depression mesially, and the occipital border is 

 excavated by a re-entering angle. The parietal bones (Plate XLII. 

 fig, 2, j3a.) are relatively small, longer than broad, and meet 

 throughout their length in the median line, excluding the supra- 

 occipital from the roof. The squamosals (fig, 2, sq.) flank the 

 parietals, forming the postero-external angle of the cranial roof, 

 and produced forwards a little along the outer margin of the 

 froutals. The frontals (figs. 2, 3 a,fr.) are very large, broad, and 

 rugose behind, tapering and nearly smooth forwards. In their 

 hinder half the median suture between them is feebly dentated ; 

 the anterior extremity of each exhibits a A-shaped excavation 

 (fig, 3 a). Occupying an indent in the outer margin of each 

 frontal above and partly in advance of the orbit is a rugose 

 elongated membrane-bone covering the prefrontal region, which is 

 perhaps best named sujyraorbital (fig. 2, sp.o.). The depressed 

 and expanded ethmoidal region (tig. 3 a, eth.) is widest at the 

 palatine articulation. The supraoccipital exhibits a large vertical 

 keel on its hinder face, but neither the occipital nor otic elements 

 are sufliciently well displayed for description. In the pterygo- 

 palatine arcade the quadrate (figs. 3, 4, qu.) is often seen. It is 

 triangular in shape, with a robust articular head, and an upwardly 

 directed process arising from the lower end of its hinder border, 

 clasping the thick styliform symplectic (fig. 4, si/m.). The whole 

 of its upper margin is apposed to the thin triaugalav metajyterygoid 

 (figs. 3, 4, m.pt.), and its anterior edge is similarlj' in contact with 

 the downwardly curved hinder extremity of the ectopterygoid (fig. 3, 

 ectp.). The twisted and expanded hyomandibidar is also shown in 

 one specimen, reaching the upper end of the symplectic ; and 

 there ai'e remains of a relatively large and thin, antero-posteriorly 

 elongated entopterygoid. In specimen no, P, 5680 there is evidence 

 of minute clustered, pointed teeth on some tliin internal bone ; and 

 this may have been either ecto- or ento-pterygoid. The maxilla 

 (figs, 3, 5, nuv.) is robust and arched, with a large upwardly 

 directed process at its anterior end and a convex oral margin. 

 The upper portion is overlapped by two large supramaxillaries 

 (figs. 3, 5, s.mx. I, 2), the hinder the deepest, and sending a 

 narrow process forwards above the upper margin of the anterior 

 plate. The pi-emaxilla, midei-lapping the maxilla, is small, and both 

 this and the maxilla are provided with very minute clustered teeth. 

 The dentary portion of the mandible (figs. 5 a, 6, d.) is very robust 

 at the symphysis, with a cluster of minute teeth in several series ; 

 the points of attachment of these teeth are shown in fig, 5 a. The 

 dentary rises in the coronoid region, and its hinder margin is 

 excavated for the reception of the large angular (fig. 6, ag.). The 

 lower border of the mandible is slightly bent inwards ; and just 

 Pboo. Zool. Soc— 1894, No. XLIV. 44 



