Branchiae pectinated, fixed, opening outwards by several distinct apertures: no opercle: jaws represented by the palatine and postmandibular bones, which alone are armed with teeth: pectorals and ventrals always present; the latter (in the male) furnished on their internal margin with long appendages.

73. Squalus

Body elongated: tail thick and muscular: pectorals of moderate size: branchial openings at the sides of the neck: snout more or less produced; with the mouth and nostrils beneath: eyes lateral.

* Snout short and obtuse: nostrils near the mouth, with a groove-like prolongation conducting to the edge of the lips; more or less closed by two membranous flaps; caudal truncated at the extremity, not forked.

(1. Scyllium). Teeth sharp and pointed, with small denticulations on each side: temporal orifices, as well as an anal fin, always present: dorsals very much behind, the first never in advance of the ventrals: branchial openings partly above the pectorals.

** Snout produced: nostrils not prolonged in a groove, nor furnished with valves: caudal with a lobe beneath, causing it to appear forked.

(2. Carcharias). Snout depressed; the nostrils beneath the middle: teeth cutting, pointed, and generally denticulated at the sides: first dorsal far in advance of the ventrals; second nearly opposite to the anal, which is always present: no temporal orifices: the last of the branchial openings above the pectorals.

(3. Lamna). Snout pyramidal; the nostrils beneath the base: teeth sharp and pointed, denticulated at the sides: first dorsal considerably before the ventrals: anal present: no temporal orifices: the branchial openings all before the pectorals.

(4. Galeus). Snout depressed; the nostrils beneath the middle: teeth sharp and pointed, with a few denticulations on the outer side only: temporal orifices, as well as an anal fin, present: the last branchial opening above the pectoral.

(5. Mustelus). Snout depressed; the nostrils beneath the middle; teeth small and obtuse, forming a closely-compacted pavement in each jaw: temporal orifices, and anal, both present.

(6. Selache). Teeth small, conical, not denticulated at the sides: temporal orifices, and anal, both present: branchial openings all before the pectorals; large, nearly surrounding the neck.

(7. Spinax). Snout depressed: teeth small, cutting, in several rows: temporal orifices present: anal wanting: branchial openings all before the pectorals: a sharp strong spine in front of each of the dorsals.

(8. Scymnus). Teeth in two or more rows; in the upper jaw lanceolate, with the cutting edges rough; in the lower jaw pyramidal, compressed, with the cutting edges crenated: temporal orifices present: anal wanting: no spines before the dorsal fins.

74. Zygaena

Head flattened horizontally, truncated in front, with the sides very much produced, appearing hammer-shaped; eyes placed at the extremities of the lateral prolongations; the nostrils at their anterior margin; mouth beneath: pectorals moderate: branchial openings at the sides of the neck.

75. Squatina

Body broad, flattened horizontally: pectorals large, extending forwards, but separated from the neck by a cleft, in which are the branchial openings: head round; mouth at the extremity of the snout; eyes above: temporal orifices present: no anal: both dorsals further back than the ventrals.

(6). Pristis

Body elongated, flattened anteriorly; with the branchial openings placed beneath: snout prolonged into a depressed sword-shaped beak, armed on each side with strong sharp spines resembling teeth: mouth beneath: temporal orifices present: no anal fin.

76. Raia

Body very much flattened, resembling a disk: pectorals extremely large, uniting with the snout, or with each other, anteriorly; extending backwards to near the base of the ventrals: mouth, nostrils, and branchial openings, beneath; eyes, and temporal orifices, above: dorsals almost always upon the tail.

(1. Torpedo). Tail short, and moderately thick: the disk of the body nearly circular; the part between the pectorals and the head and the branchiae furnished with an electrical apparatus: teeth small and sharp.

(2. Raia). Tail slender; furnished above, towards its extremity, with two small dorsals, and sometimes the vestige of a caudal: disk rhomboidal: teeth slender, close-set, arranged in a quincuncial order.

(3. Trygon). Tail slender; armed with a sharp serrated spine, but without fins: head enveloped in the pectorals, which meet at an obtuse angle: teeth slender, set in a quincuncial order.

( Myliobatis. ) Tail long, and extremely slender; armed with one or more serrated spines, and also furnished, near its base, with a small dorsal: head projecting from between the pectorals, which last are much broader transversely than in the preceding sub-genera: jaws with broad flat teeth forming a pavement.

(4. Cephaloptera). Tail long, and extremely slender; armed with a spine, and also furnished at its base with a small dorsal: head truncated in front, placed between two horn-like prolongations of the pectorals, which are broad as in the last sub-genus: teeth small, and very slender, finely denticulated.