Branchiae pectinated, free, with one large external aperture; furnished with an opercle, but without rays in the membrane: upper jaw formed by the palatine bone firmly united to the maxillary: intermaxillary rudimentary.

71. Acipenser

Body elongated; mailed, as well as the head, with osseous tubercles arranged in longitudinal rows: snout conical: mouth placed beneath, very protractile, small, without teeth: nostrils and eyes lateral: four pendent barbules on the under surface of the snout.