706 DR RAMSAY H. TRAQUAIR S DESCRIPTION OF 



wards, by reason of the wide extent of the gape, and the consequent very posterior 

 position of the articular end of the lower jaw. 



The suboperculum (36) is nearly square, but its posterior margin is longer 

 than the anterior one, which though also directed somewhat backwards, is not 

 so much so as the anterior margin of the previous bone, with which it conse- 

 quently forms a slight angle. 



I have looked in vain for any very distinct representatives of the preoper- 

 culum and interoperculum of other fishes. On referring to fig. 2, it will be seen that, 

 in front of the operculum, follows the triangular plate (g) covering the cheek, a 

 small portion of the suspensory apparatus of the lower jaw being exposed between 

 them above ; while in front of the suboperculum follows the hinder border of the 

 upper jaw. If present, the bones in question must then be reduced to very 

 narrow laminae, so as to render their recognition very difficult, at least in the 

 state of preservation in which these fossils usually occur. 



Hyoid bone and branchiostegal rays. — What I consider to be the posterior part 

 of the body of the hyoid, may be seen in fig, 1, h, with four of the branchiostegal 

 plates behind it. The latter are also shown in fig. 2, the lower ones being broken 

 off behind, so as to expose the underlying coracoid (52). None of my specimens 

 show the branchiostegal rays in complete series, so that their number cannot be 

 exactly ascertained. In one example I counted at least twelve ; and there can 

 be no doubt that there were a great many more, probably one-half as many 

 more again. They take the form of oblong imbricating plates, whose posterior 

 margin is broader than the anterior one. One of the upper plates in fig. 2. 

 measures 9 lines in length, and 5 lines in breadth, at the hinder border. 



In front of the operculum, and above the posterior part of the superior max- 

 illary bone, is a triangular plate (g) with the acutely-pointed apex directed back- 

 wards in the angle between the two bones just named. Between it and the 

 operculum above may be seen, as already remarked, a portion of the suspensorium 

 of the lower jaw exposed. This plate may be a member of the " Gesichtspanzer," 

 representing the cuirass of small plates behind the eye and in front of the oper- 

 culum of Lepidosteus. It will also be seen to have exactly the same relative 

 position to the other bones of the head, as the bone covering the cheek and 

 masticator}' muscles in Polypterus, and which by Agassiz and Muller is reckoned 

 as " preoperculum ; " by Huxley as " supratemporal." 



In front of this plate is a sickle-shaped suborbital bone (73), surrounding the 

 posterior and lower margin of the orbit, and likewise fitting on to the lunated 

 anterior-superior part of the superior maxillary bone. There are doubtful indi- 

 cations of another, just behind the upper margin ; the rest of the chain are crushed 

 inwards, and concealed beneath the ironstone matrix. On examining some other 

 heads, however, it seems probable that the eye was completely surrounded, as in 

 Lepidosteus, by a chain of such narrow ossicles. 



Shoulder-girdle. — Above the operculum, and behind the mastoid and parietal 



