OSMEROIDES. 



115 



torily the principal characters of the species. It is supplemented by a fine series 

 of specimens in the British Museum, but the species is not yet well represented in 

 other collections. 



Apart from its roof, the cranium is imperfectly known. The supraoccipital, 



-<->i 









Fig. 38. Osmeroides lewesiensis (Mantell) ; restoration, about one third nat. size. — English Chalk. 



which bears a prominent median keel on its hinder face, extends as far forwards 

 as the frontal bones (B. M. no. P. 5680), but is completely covered by the parietals. 

 The well-ossified epiotics, which form a slight backward prominence on each side, 

 are also completely covered by the roofing bones. The side of the cranium 

 beneath the articulation for the hyomandibular is impressed by a deep and 

 extensive subtemporal fossa, as in Elops (well seen in B. M. no. 39433). There is 

 a roofed posterior temporal fossa, as usual in the Elopidae. The flattened roof of 

 the cranium, with its characteristic ornamentation, is shown in PI. XXIII, figs. 

 2 a, 3. The parietal bones (pa.) are relatively small, longer than broad, and meet 

 in a wavy suture in the middle line throughout their length. The squamosals (sq.) 

 flank the parietals and are produced a little in front of them along the outer 

 margin of the frontals. A small radiately rugose supratemporal plate (st.) 

 overlaps the posterior border of each squamosal. The frontals (fr.) are very 

 large, broad, and radiately rugose behind, tapering and nearly smooth forwards. 

 In their hinder half the median suture between them is wavy, while in the smooth 

 portion it is straight. The anterior extremity of each frontal, where it overlaps 

 the mesethmoid, exhibits a A-shaped excavation. The smooth mesethmoid (eth.) 

 ends in front in a rhomboidal expansion, which is about two thirds as long as 

 broad. On either side of the frontal region, above and partly in advance of the 

 orbit, an indent is occupied by an elongated, ovoid membrane-bone, which is 

 radiately rugose and must probably be interpreted as a supraorbital (spo.). The 

 cheek is completely covered with bony plates, which are thinner than all the other 

 external bones except the gular plate, and have often lost their ornament by 

 flaking in the fossils. Three large trapezoidal plates (fig. 2, po.) bound the orbit 

 posteriorly and postero-inferiorly. They are traversed near their orbital border 

 by a large slime-canal, from which branches appear to radiate among the coarse, 



