282 NORTHERN ZOOLOGY. 



sures an inch and a half, or nearly as much as the distance between the anterior nostrils and 

 the tip of the snout : when the jaws are retracted the commissure of the mouth is transverse, 

 and is drawn considerably within the under surface of the head. The lips, thin and pendu- 

 lous at the junction of the jaws, are separated by a fissure on the medial line of the upper jaw 

 and are altogether wanting on the middle half of the lower jaw. The tongue is fixed, pro- 

 minent, and smooth, and there are no teeth whatever. The orbits are small and circular and 

 the nostrils large, particularly the posterior openings. Four lengths and a half of the head 

 are equal to the entire length of the fish. 



The Gill-cover consists of a pretty large operculum, which has a form more like that of 

 A. schipa than any of the other figures in Lovetsky's monograph*: a chain of three smaller 

 bony plates proceeding from the lower corner of the operculum gives firmness to the gill- 

 membrane, which is not to be distinguished from the softer parts of the gill-cover. 



Skin. — The whole upper surface of the head is encased in bony plates of various forms, 

 which are rough, with radiating, granulated ribs : the plates on the snout admit of a little 

 motion, the others are fixed; a few small ones exist on the tip of the bone beneath the snout, 

 and farther back rises into two tubercles. The suborbital' bones, humerals, and scapulars, 

 have surfaces still more rough than the upper plates, in conjunction with which they 

 form a firm helmet that compensates for the too great flexibility of a cartilaginous cra- 

 nium. The shields on the body have rough saddle-shaped bases, with very acute central 

 ridges terminating in a hook or spine which points backwards, and is longest and most acute 

 on the posterior dorsal shields ; there are also some serratures on the ridge of the shields 

 beneath the point of the spine. The dorsal row contains fourteen shields, exclusive of one 

 without a spine, which is incumbent on the first ray of the dorsal fin : the anterior of these 

 shields is fixed among the plates of the head, the others move with the skin, and are near each 

 other, though not in actual contact. The shields on the lateral lines have lozenge-shaped 

 bases, placed obliquely, and are smaller and farther apart than the dorsal ones anteriorly, but 

 the posterior ones successively diminish and approximate until they reach the curvature of 

 the tail, beyond which they cannot be easily reckoned, though they can be traced in form of a 

 cartilaginous line extending along the under margin of the tail to its tip : excluding the 

 extreme caudal ones, then, there are in this specimen forty-two lateral shields on the left side, 

 and forty-seven on the right. The ventral shields, of which there are eleven on the left side, 

 and nine on the right before the ventrals, are wider apart than the lateral ones, and of 

 an intermediate size between them and the dorsal ones. There are also five or six sub- 

 orbicular, spineless plates in two rows, between the vent and anal fin, one on the commence- 

 ment of the latter, and another on the upper ray of the caudal. The compressed, turned up 

 part of the tail is covered above the lateral line by ten or eleven crowded rows of small, rough, 

 lozenge-shaped plates, which give it a reticulated appearance. The rest of the skin is studded 

 with small, scattered, stellated tubercles of various forms and sizes; some exist even on the 



* In Professor Lovetsky's monograph on Russian sturgeon, no statement is given of the parts that are included under 

 t he name of snout, so that we cannot compare the length of this member in our fish with that of his. 



