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 fins weakly concave (curving inwards) rear margin, and the pectoral finss outer margin is slightly convex (curving outwards), and both fins are weakly falcate.