Pteroplatea Müller and Henle, 1837.
P. marmorata, Cooper, State Collection, Species 674. [[Fig. 25.]]
Fig. 25.
Specific characters.—Outline of disk rhomboidal, the anterior borders forming an obtuse angle in front, nearly straight in their course to the lateral angles, which are sub-acute; the posterior borders rounded.
Ventrals small, oblong, obtuse-angled, projecting a little behind the disk. Tail nearly twice the length of ventrals, slender and pointed, flattened laterally behind the spine, and bordered by a very narrow membrane, commencing opposite the end of the spine below, and ending a little farther back above.
Spine arising at a point one-third the length of the tail from its base, one-sixteenth of its length, and less than a fourth as wide as it is long.
Both surfaces are nearly flat.
Proportional measurements:
| Total length of specimen, 9½ in. | 100. |
| From median line to tip of pectoral | .80 |
| From anterior angle to eyes | .13 |
| From anterior angle to ventrals | .70 |
| Antero-posterior length of ventrals | .10 |
| Length of claspers | .04 |
| Length of tail beyond ventrals | .25 |
| Length of caudal spine | .04 |
| Distance between eyes | .15 |