Description of Mustelus hacat: this species differs from its congeners in having a uniformly dark gray brown color above and conspicuously having white tips and trailing edges of the dorsal, pectoral, anal, and caudal fins. Although some specimens of M. lunulatus and newborn pups and juveniles of M. canis from the western Atlantic, have tips and trailing edges of first dorsal, pectoral, anal, and caudal fins transparent or pale white, they clearly differ from this species in having less contrasted dorsal color compared with tips and trailing edges of the fins. Mustelus hacat is distinguished from the other eastern North Pacific species of Mustelus in having: 1) upper jaw teeth cuspidate and distinctly asymmetric, with low rounded cusp (teeth of californicus and lunulatus are from molariform to cuspidate and slightly asymmetric, with blunt to low rounded cusp, whereas henlei

and dorsalis have cuspidate and slightly asymmetric, with high sharp cusp teeth); 2) upper jaw labial folds notably longer than the lower folds, only similar to henlei (californicus has upper and lower jaw labial folds about equal in length, lunulatus has upper jaw labial folds notably shorter than lower jaw labial folds, and dorsalis has upper jaw labial folds slightly longer than lower jaw labial folds); 3) posterior margin of first dorsal fin vertical from apex, only similar to lunulatus, californicus, henlei, and dorsalis have the first dorsal fin with sloping posterior margin); 4) inter-nostril space wide (49-58 vs. 33-49% pre-oral length for all other four species); and 5) inter-orbital space wide (5.6-6.8 vs. 4.3-5.6% TL for californicus, henlei, lunulatus, but similar to dorsalis 5.7-7.5% TL) (Ref. 30948).