76 ANNUAL REPORT OF 



tance in advance of the upper tier. Indications of a mucous 

 canal are observable over part of the circumorbital ring in some 

 species. Immediately beneath the latter is situated a series of 

 suborbitals, which are much larger and less numerous than those 

 of Lepidotus, Dapedius and related genera. Evidence of 

 specialization is observable here, these large plates having no 

 doubt resulted from the fusion of smaller ones. The boundaries 

 between the suborbitals and contiguous plates have not been 

 satisfactorily determined even in the best preserved individuals. 

 The postorbital, or "plaque buccale" of Agassiz, is a large thin 

 plate on either side of the head, situated between the circumor- 

 bitals and the operculum. It is sometimes in contact with the 

 latter plate posteriorly, as in S. bergeri and possibly also' in 

 S. nilssoni (although it may have been displaced in the type so 

 as to come to occupy this position accidentally), or in other 

 cases it may be entirely separated from it by the preoperculum, 

 as in S. capensis. 



The opercular apparatus consists of ( I ) a large operculum, of 

 variable shape, but generally with a narrower upper border; (2) 

 a narrow, falciform preoperculum, with the mucous canal inter- 

 rupted and appearing as a series of perforations; (3) a sub- 

 operculum, the exposed surface of which generally exhibits a 

 sublunate outline; and (4) a triangular interoperculum. The 

 posterior borders of the operculum and interoperculum are em- 

 braced by a large and heavy plate, often very conspicuous, the 

 clavicle. This is similar to' the preoperculum in form, but is much 

 more solid, and its terminal angle in front is frequently thickened 

 or otherwise prominent. It is succeeded behind by one or two 

 enlarged postclavicular scales. There is a series o>f branchiostegal 

 rays, but these, like the coracoid, are seldom well preserved, 

 and hence not satisfactorily known. The dental characters have 

 been indicated with sufficient fulness in the preceding family and 

 generic diagnoses. 



In the following systematic discussions, conscientious regard 

 has been paid to- the opinions of Professor Newberry, and none 

 of the changes here introduced can be said to be inharmonious 

 with his views, implied or expressed. But it is clear to everyone 

 that this author, with all his clarity of perception, did not always 



