ACJPENSER NASUS. 407 



breadth are equal, and then they become narrower. The margins of their 

 bases are serrated. There are five shields behind the dorsal fin, of which the 

 middle plate is the largest. The lateral row, which is not placed so high on 

 the side as in some other forms, consists of from thirty-two to thirty-four 

 lozenge-shaped shields, which are small, elongated vertically, and distant 

 from each other; they are keeled longitudinally, and the keel rises into a spine. 



The ventral shields, eight or nine in number, are round and have similar 

 keels. There are two shields in front of the anal fin, and two more behind. These 

 are unequal in size ; the two most distant from the fin are the larger. 

 Between the rows of shields the skin is densely filled with small star-shaped 

 scales, which become lozenge-shaped on the breast, where they are arranged in 

 lines. 



The pectoral fin is short and rounded ; its bony ray is no longer than the 

 width of the skull over the squamosal bones. The ventral, dorsal, and anal fins 

 are obliquely truncate, and the dorsal is as high as the anal. 



The caudal fin is not well developed, but its upper lobe is as long as the 

 head. 



Acipenser nasus (HECKEL). 



This is another Adriatic Sturgeon, found in the River Po and the lagoons 

 of Venice, and brought, according to Heckel, to the Venice fish-market, with 

 other species, in autumn. 



It appears to be rare, since Heckel possessed but one specimen, twenty-six 

 inches long, and the species is not represented in the collection of the British 

 Museum. 



The colour of the body is brown above, with the head paler. 



The proportions of the body are very similar to those of A. heckelii, 

 the breadth being equal to the height, and this measurement is about one- 

 ninth of the length of the fish, while the head is one-fifth of the total length. 

 The snout contracts regularly in front of the eyes to a narrower lanceolate form 

 than in the other species ; and the part of the head which lies in front of the 

 anterior narines would form nearly an equal-sided triangle. The profile, seen 

 from the side, rises concavely to the back of the head, which is convex trans- 

 versely. The shields of the head are chiefly remarkable for the immense size 

 of the ethmoid, which reaches from the extremity of the snout back between 

 the frontals, and its extremity just penetrates the points of the parietals. The 

 condition of this plate would, therefore, justify us in regarding all the small ossifi- 

 cations upon the snout in other species as divisions of the ethmoid (Fig. 197). 



The first dorsal shield is remarkably broad, being only a little narrower than 

 the transverse width of the two parietals. The supra-occipital is T-shaped, 



