OSMEROIDES. 117 



antero-superior angle. The interoperculum is small, smooth, and almost or 

 completely covered by the lower limb of the preoperculnm. The latter element 

 (fig. 2, pop.) is sharply angulated, moderately expanded, deeply channelled by the 

 slime-canal, and marked with a few radiating rugae. The branchiostegal rays 

 (br.) are not less than eighteen in number, the uppermost being large, broad, and 

 rugose ; five are borne by the epihyal. The gular plate (fig. 1, gu.) is remarkably 

 thin and elongated, always smooth. 



In the axial skeleton of the trunk, the vertebral centra are strengthened by 

 secondary calcifications in the form of small irregular longitudinal ridges (PI. 

 XXIII, fig. 7). Those of the anterior abdominal and hinder caudal regions are 

 deeper than long, while the remainder are about as long as deep. The arches are 

 imperfectly known, but, as shown by Agassiz, op. cit., pi. lx c, figs. 5, 6, those of 

 the centra towards the base of the tail are especially stout. Some styliform bones 

 in the abdominal region of B. M. no. 49892 appear to be intermuscular elements. 



In the pectoral arch, a long and narrow post-temporal bone impinges on the 

 epiotic angle of the skull. It is only marked by a few coarse horizontal rugae at 

 its postero-inferior angle (B. M. no. 4296). The supraclavicle and clavicle are 

 quite smooth ; and no postclavicle has been seen. The pectoral fin-rays (PI. 

 XXIII, fig. 1, pet.), which are at least fourteen in number, are un jointed for a 

 considerable distance proximally, and the foremost ray (shown in B. M. no. 

 41894) exhibits an oblong expansion at its base of attachment. The rays of 

 the pelvic fins {ph.), not less than eleven in number, are similarly only divided 

 quite at the distal end, while the foremost is especially stout. The dorsal fin, 

 placed in the middle of the back, opposite to the pelvic pair and arising somewhat 

 in advance of the latter, is incompletely known, but consists of robust rays which 

 are unjointed for a long distance proximally though very closely divided at the 

 distal end. The supports of the dorsal fin-rays (shown in B. M. no. 49892) are 

 large and dagger-shaped, having wide "wings." The anal fin (fig. 1, a.) is small 

 and remote. The caudal fin appears to have been forked, and its rays are very 

 closely articulated. 



The scales (PI. XXIII, figs. 1, 8) are in regular, uniform series, and very 

 deeply overlapping. Their posterior border is gently rounded, while their anterior 

 border is truncated. As a rule, they are more or less flaked or abraded in the 

 fossils, and their exposed portion is nearly smooth or shows only the concentric 

 lines of growth, while their covered portion is marked by a few radiating grooves, 

 which terminate in notches at the anterior truncated border. "When exceptionally 

 well preserved (fig. 8) their exposed portion is ornamented with radiating lines of 

 fine tubercles, while the grooves on their covered portion are obscured by a still 

 more minute granulation. The scales of the lateral line are not enlarged or 

 thickened ; but most of them are marked by a feeble smooth ridge, which ends at 

 a notch in the hinder border. 



