16 ACIPENSERUXZE. 



closely cover the whole upper surface of the snout, sepa- 

 rate the frontals wholly from each other. The osseous 

 centres of the temporal shields are somewhat nearer to 

 the tip of the snout than those of the coronals are. On 

 the left side of the specimen a small squamosal interposes 

 between the temporal and mastoid shield, but on the other 

 side this piece is confluent with the temporal. A mode- 

 rate inclination of the surfaces of the coronals towards 

 the mesial line makes a longitudinal furrow, which disap- 

 pears anteriorly, the interfrontal plates being nearly flat, 

 and the snout flatly convex transversely. Much of the 

 gill-flap is occupied by the large opercular shield, which 

 is marked by pits and furrows, with thin intervening 

 crenated walls distinctly radiating from a point near the 

 posterior edge of the plate. This shield being visible 

 from above merely in profile is not represented in the cut. 

 Behind and beneath the eye there is a rough rectangular 

 chevron which, in form and position, represents the pre- 

 operculum of osseous fishes. On the under surface of 

 the snout a raised ledge, narrow at the barbels and widen- 

 ing gradually in running forwards, as in the Ac. sturio of 

 Heckel, is covered either by a single slightly-rough plate, 

 or by several coalescent ones. The humeralv*plate is 

 deeply pitted, and the coracoid is marked by distinctly- 

 radiating furrows and pits. 



The body-shields are radiately furrowed and pitted, 

 and have thin longitudinal crests. Eleven saddle-formed 

 shields occupy the ridge of the back before the dorsal 

 fin, the fourth or fifth of the series being the largest, and 

 the ridges of all highest in the middle. The scalene 

 lateral shields, lying between the suprascapular and 

 caudal fin, are thirty in number. In other specimens 

 their number varies from twenty-nine to thirty-two, there 

 being generally more on one side of the fish than on the 



