This tribe falls into four groups, so far as the Gulf of Maine fauna is concerned: first, the torpedoes (family Torpedinidae), with large caudal fin, interesting because provided with electric organs capable of giving a strong shock; second, the skates (family Rajidae), with very thin bodies, comparatively short tails without tail spines, and only a trace of caudal fin; third, the sting rays (families Dasyatidae and Rhinopteridae), with long whiplike tails armed with-a stiff saw-edged spine (or-spines); and fourth, the devil rays (Mobulidae) with two ear-like fins extending forward from the front of the head. Most of our common species belong to the second group.
Among torpedoes, skates, and rays, fertilization is internal as it is among sharks, and the modification of the posterior edges of the pelvic fins into rodlike semitubular claspers (the copulatory organs) distinguishes males and females at a glance. Some bear "living" young, ready for independent existence; others lay eggs.
| KEY TO GULF OF MAINE SKATES AND RAYS | |||
|---|---|---|---|
| 1. | The front of the head bears a pair of separate, ear-like fins, extending forward | — | Devil ray, p. 77 |
| The front of head does not bear a pair of separate ear-like fins extending forward | 2 | ||
| 2. | There is a large triangular caudal fin as well as two well developed dorsal fins on the tail | — | Torpedo, p. 58 |
| There is no distinct caudal fin; the dorsal fins, if any, are very small | 3 | ||
| 3. | No long dorsal spine on tail | 4 | Common skates |
| There is a long saw-edged dorsal spine (or spines) on the tail | 11 | ||
| 4. | The upper surface of the disc is marked with conspicuous black rosettes | — | Leopard skate, p. 66 |
| The markings on the upper surface of the disc are not in the form of black rosettes | 5 | ||
| 5. | There are no conspicuous thorns along the mid-dorsal zone of disc between the spiracles and the base of tail; the lower surface of disc is marked with black dots or dashes, marking the openings of the mucous pores. | — | Barndoor skate, medium sized and large specimens, p. 61 |
| There are one or more rows of conspicuous thorns along the mid-dorsal zone of disc rearward from the spiracles; the lower surface of disc is not marked with black dots or dashes | 6 | ||
| 6. | There are no large thorns on the rear 1/4—1/3 of tail | — | Smooth-tailed or Prickly skate, p. 70 |
| There are one or more rows of large thorns along the rear part of tail as well as farther forward along it | 7 | ||
| 7. | There are no large thorns on upper side of disc between the spiracles and the level of axils of pectoral fins | — | Barndoor skate, very small specimens, p. 61 |
| The upper side of disc, rearward from spiracles, has more or fewer large thorns | 8 | ||
| 8. | The thorns of the midrow on the tail are much larger and more conspicuous than any other thorns on the tail, and not more than 9 or 10 in number | — | Thorny skate, p. 72 |
| No one row of thorns along the tail is much larger or more conspicuous than the other thorns on the tail; there are at least 15 thorns in each of the rows along tail | 9 | ||
| 9. | There is only one row of large thorns along the midzone of the disc from the nape to the level of the axils of the pectoral fins; the first and second dorsal fins are separated by a definite space or at least by 1 or 2 thorns; the forward angle of the disc is less than 110°; the upper surface of the disc is marked with short dark bars as well as with roundish spots | — | Brier skate, p. 65 |
| There are at least three rows of thorns along the mldzone of the disc from the nape to the level of the axils of the pectoral fins; the first and second dorsal fins are not separated by a definite interspace or by a thorn or thorns; the forward angle of the disc is more than 125°; the upper surface is not marked with dark bars though it is variously spotted | 10 | ||
| 10. | Upper teeth in at least 72 series, most often 90-100; does not mature sexually until at least 26 inches long. | — | Big skate, p. 63 |
| Upper teeth in not more than 66 series and usually less then 54; matures when only 18-20 inches long. | — | Little skate, p. 67 | |
| 11. | There is a small dorsal fin on the upper side of the tail, in front of the spine (or spines); the crown of the head is high-domed, with the eyes and spiracles on the sides; there are only 7-9 series of teeth in the form of large flat grinding plates | — | Cow nosed ray, p. 76 |
| There is no dorsal fin on the tail; the crown is low, flat, and with the eyes and spiracles on the upper surface; the teeth are in many series, in mosaic arrangement | — | Sting ray, p. 74 | |