_Mesoplodon stejnegeri_: Yaquina Bay, near Newport, Oregon. February 15 (?), 1904. Adult. Skull in the National Museum. _Ziphius cavirostris_: Kiska Harbor, Alaska. September, 1904. Known only from photographs. _Berardius bairdii_: St. George Island, Pribilof Group, Alaska. June, 1903. Adult female. Skeleton in the National Museum. St. George Island, Pribilof Group, Alaska. June, 1903. Young male. Skeleton in the National Museum. Centerville Beach, near Ferndale, California. October, 1904. Adult male. Skeleton in the National Museum. Alaska or California (?). Skull formerly in museum of the Alaska Commercial Company, San Francisco. Trinidad, California. January 30, 1905. Not preserved; perhaps not this genus. St. George Island, Pribilof Group, Alaska. August 21, 1909. Female. Probably not preserved. Reported by Maj. Ezra W. Clark. DESCRIPTIONS OF SKULLS AND SKELETONS OF ZIPHIOID WHALES. Genus MESOPLODON Gervais. Of this genus the National Museum has four specimens; namely, (1) a skull (Cat. No. 21112, U.S.N.M.) obtained at Bering Island, North Pacific Ocean, in 1883, by Dr. L. Stejneger, and made the type of the species _M. stejnegeri_ True; (2) a skull and photographs (Cat. No. 143132, U.S.N.M.) of the same species, from Yaquina Bay, Oregon, obtained in exchange from Mr. J. G. Crawford in 1904; (3) a skeleton, cast, and photographs of a young male (Cat. No. 23346, U.S.N.M.), hitherto supposed to represent _M. bidens_, caught at Atlantic City, New Jersey, in 1889; and (4) a skeleton of an adult (Cat. No. 49880, U.S.N.M.) from the Chatham Islands, New Zealand, representing _M. grayi_.[1] In addition to this material, I have had the privilege of examining two skulls belonging to the Museum of Comparative Zoölogy, and hitherto supposed to represent _M. bidens_, and two skeletons belonging to the American Museum of Natural History. Of these last, one is that of an adult and was purchased by the American Museum under the name of _M. layardi_, but was subsequently recognized to be a new species and was described by Mr. Andrews, under the name of _Mesoplodon bowdoini_. The other is that of a young individual, and has been labeled _M. grayi_. As already noted by Dr. G. M. Allen,[2] only four specimens of _Mesoplodon_ have been recorded hitherto from the Atlantic coast of the United States. These are: 1. An adult, sex unknown, but probably female, 16 feet long, found at Nantucket, Massachusetts, in 1867, and recorded by Prof. L. Agassiz.[3] The skull of this individual is in the Museum of Comparative Zoölogy, Cambridge, Massachusetts. 2. A young male, 12½ feet long, captured at Atlantic City, New Jersey, March 28, 1889. The skeleton (Cat. No. 23346, U.S.N.M.) is in the National Museum.