of Ampliicentrum granulosum. 279 



centres of ossification seem placed near their anterior-superior 

 and anterior-inferior angles respectively. In front of these 

 two bones, and covering a portion of the cheek between them 

 behind and the maxillary and suborbitals in front, is a pretty 

 large vertical plate (p.op) , which occupies a position similar 

 to that of the great praeopercular cheek-plate of Polypterus. 

 A precisely similar plate occurs in Eurynotus and in Platy- 

 somus ; and there is also a quite analogous one in the Palaeo- 

 niscid?e, though differing somewhat in form. Dr. Young has 

 stated that an interoperculum is present, nearly equal in size 

 to the operculum, and which " overlaps the branchiostegals, 

 which are nevertheless enamelled externally." In none, how- 

 ever, of the heads of Amphicentrum which I have examined 

 (many of them exceedingly well preserved in this region) have 

 I ever seen any evidence of any such bone. 



The branchiostegal rays (br, figs. 1-3) form a series of flat, 

 oblong, imbricating plates, with finely tubercular enamelled 

 surfaces, which follow immediately upon the lower margin of 

 the suboperculum. They gradually diminish in length as 

 they pass downwards and forwards ; and in front an arrange- 

 ment quite similar to that seen in Eurynotus and in the 

 Palseoniscida? is observable : viz., the anterior plate of each 

 series is much broader than the rest ; and between these and 

 behind the symphysis of the jaw is a median lozenge-shaped 

 one. 



Circumorbital ring. — The presence of a narrow chain of 

 small supraorbital plates (sr.o, fig. 3) is evident in several 

 specimens, though their number is not determinable. The 

 same must be said of the subo7'bitals (s.o, figs. 1, 2, & 3), 

 the chain of which, attached above to the postfrontal, seems 

 to be very narrow behind. In several specimens a well-marked 

 suborbital of an elongated form is seen, as in fig. 3, curving 

 round the orbit behind ; and at the anterior-inferior part of 

 the orbit, and above the front part of the maxilla, is a very 

 large one (figs. 1 & 2), like the so-called lacrymal of most 

 osseous fishes. 



Shoulder-girdle. — Attached to the posterior part of the 

 skull, behind the squamous plate, and passing downwards 

 and slightly backwards, largely overlapped by the operculum, 

 is a powerful supraclavicular (s.cl, fig. 1). It is broad above, 

 getting narrow below, and, like the corresponding bone in the 

 Palseoniscidae, is perforated by the lateral slime-canal. The 

 presence of an upper supraclavicular (suprascapular , Owen) is 

 not very clear ; there is, indeed, a small plate above the last- 

 described bone and behind the parietal, which may, however, 



