of the Sharks: the dorsals are two, sometimes three in number, small, and placed very far back upon the slender tail; sometimes, indeed, close to its extremity; a minute caudal is occasionally seen, but more frequently wanting; the dorsals also are, in some species, obliterated.
The eyes, and the temporal spiracles, are placed on the upper surface: the latter are much larger than in the Sharks, often exceeding the size of the eyes; they communicate internally with the mouth and gills. The mouth, the nostrils, and the gill-openings are placed on the under-surface, and quite concealed from view in the ordinary position of the fish as it flounders along on the bottom of the sea. The gill-openings agree with those of the Sharks in number, form, and structure. The mouth is small, and set with numerous teeth, which are arranged in close array like paving-stones; they are more or less square, and flat; but in old males, the middle ones assume a pointed form, overlapping one another, and pointing backward towards the throat.
As in many of the Sharks, the eyes are furnished with a nictitating membrane, or skin, which can be drawn over the eye-ball at pleasure, serving the purpose of an eyelid.
The young of the Rays are enveloped at birth, like those of some of the Sharks, in capsules of thin horn or leathery substance. They are generally more square in form, with the angles produced, but not attenuated to long filaments. The accompanying figure represents the egg-capsule of the Common Skate, frequently found on our sea-beaches, and commonly called Skate-
