1.8 ACIPENSERIDJl. 



being a flat, longitudinally-oval plate resembling the dorsal 

 shields in size and texture, but having a small posterior 

 peak, which rises as the first of the rays. About six 

 stumps, seemingly bony and gradually increasing in height, 

 follow it, and are incumbent on each other and on the 

 flexible rays. Behind the dorsal two heart-shaped plates 

 follow one another 011 the ridge of the tail. The anal, 

 which in this specimen has been injured posteriorly, con- 

 sists in others of twenty-five rays, the first being very 

 short and incumbent, and in fact the peak of an oblong 

 flat plate, as in the dorsal. Between this plate or fulcrum 

 and the vent there are three pairs of small shields. An 

 upper low caudal fin is composed of a long strap-shaped 

 rough plate with a posterior peak, and of eighteen or 

 nineteen firm, slender, jointless rays lying closely tiled 

 on one another. Underneath these inflexible rays there 

 is a triangular lateral space on each side, which is densely 

 covered by rough, keeled, bony eminences. The under 

 portion and main part of the caudal is lobed anteriorly, 

 and contains numerous jointed rays. In young individuals 

 the anterior under lobe is said not to be developed. The 

 pectoral contains thirty-eight rays, which are prickly on 

 the edges, and the first one is stout and bony, seem- 

 ingly formed by the coalescence of about ten rays, whose 

 number is shown by the prickly ridges which rib its 

 surface. 



Dr. James McBain, of Leith, possesses the head of a 

 Sturgeon that was caught near Stirling, in which the 

 cranial plates correspond almost exactly with those of the 

 specimen described above, except that the squamosals on 

 both sides are coalescent with the mastoidal shields. In 

 this preparation the thin vertical plate of bone which 

 descends from the mastoidal shield into the cranial car- 

 tilage is well shown. Dr. McBain's fish seems to have 



