sentence: The pelvic fin weakly concave (curving inwards) rear margins, and the pectoral fin's outer margin is slightly convex (curving outwards), and both fins are weakly falcate.
modified: fix grammar: The pelvic fin weakly concave (curving inwards) rear margins, and the pectoral fin's outer margin am slightly convex (curving outwards), and both fins is weakly falcate.