8 



rally in a joint furnished with a trochlear cartilage, and 

 moving on the wing-like process of each palatine. A 

 thick fleshy lip, sometimes lobed, covers the premaxil- 

 laries ; but the mandibular lip is deficient in some groups 

 of species, except at the corners of the mouth ; and in 

 other groups the posterior lip crosses the orifice, either 

 in form of a continuous soft roll, or with a mesial depres- 

 sion, or even a mesial interspace The fulness of the 

 Lips, in conjunction with the forms of the dorsal crests 

 and a few other characters, have been made to serve for 

 grouping the species. The gills, as in the osseous fishes, 

 consist of five movable arches, and are comb-like, with 

 free tips : a pectinated accessory gill also adheres to the 

 inner surface of the gill-cover, and there is a small spout- 

 hole close behind and above it. 



Of the five rows of bony shields on the body, one pro- 

 tects the ridge of the back from the occiput to the dorsal 

 fin ; a lateral row extends on each flank from the shoul- 

 der to the caudal fin ; and a row on each side of the belly 

 ends at the ventrals. Each dorsal shield is more or less 

 distinctly keeled by an acute longitudinal crest, whose 

 apex, in some groups of species, overhangs the posterior 

 edge of the shield, but in other groups is central, the 

 plate sloping off from it both before and behind. The 

 skin intervening between the rows of shields varies also in 

 character, being naked and smooth, or studded with bony 

 grains, either of a granular form, or star-shaped, or with 

 acute points or even hooks. In Ac. Guldenstddii of 

 Brandt, which is the Ac. sturio of Pallas, the skin of the 

 breast between the coracoid shields is set with elevated 

 star-like or roundish and denticulated ossicles ; while in 

 Ac. nasus of Heckel the same region is closely covered 

 with flat ganoid scales, like those of Lepidosteus. In Ac. 

 schypa of Giildenstadt the same part shows stellate ossicles, 



