THE COMMON BllTTISH STURGEON. 15 



when laid back do not reach the latter. They are taper- 

 ing and roundish, but in the dry state show a furrow as 

 if they were composed of two binate cartilaginous rays. 

 Other Frith of Forth specimens do not exhibit this fur- 

 row. The lips, having shrunk so that their true form 

 cannot be ascertained, are not described. Shields or buck- 

 lers, closely connected by suture, cover the whole dorsal 

 aspect of the head. They are deeply pitted, the pits 

 being only partially disposed in rows so as to form radi- 

 ating furrows. These well-defined depressions are sepa- 

 rated by thin walls, which are crenulated, but do not rise 

 above the general level, so that the character of the sur- 

 face is not granular. The osseous centres of most of these 

 shields may be made out, but they do not rise into acute 

 crests as in the young fish. Certain lines or ledges are 

 visible rather by their smoothness than by their elevation, 

 and the most remarkable of them present the profile of an 

 obelisk whose apex is in the centre of the occipital shield, 

 whence short lines deflect on each side to the osseous cen- 

 tres of the coronals. Lines proceeding from thence to the 

 centres of the frontals form the sides of the obelisk. Other 

 less conspicuous lines radiate from the same centres of 

 the frontals, namely, backwards over the temporals, and 

 forwards towards the nasal regions, with a convergence 

 coincident with the narrowing of the snout. The poly- 

 gonal occipital shield receives the anterior point of the 

 first dorsal shield into a sharp mesial notch, and emits 

 anteriorly a salient acute process that enters between the 

 coronals for nearly one half of their length, these plates 

 coming in contact with each other for only about a third 

 of their length, and having the point of an interfrontal 

 plate insinuated between their anterior ends. This ob- 

 long interfrontal, and two other intercalary pieces, larger, 

 but otherwise similar to the polygonal shields which 



