Ft. In. Lines. Total length (measuring along the curve of back) 5 4 0 Length from tip of muzzle to vent 3 10 9 to dorsal fin 2 6 5 to pectoral 1 4 5 to eye 0 9 9 to breathing aperture (following curve of head) 0 10 7 to angle of mouth 0 7 9 of dorsal fin along the anterior margin 1 0 5 Height of do. 0 6 4 Length of pectoral, along anterior margin 1 2 8 Width of tail 1 4 5 Girth of body before dorsal fin 3 0 6 before pectoral fin 2 8 2 before tail fin 0 7 8 of head over the eyes 2 0 0 Habitat, coast of Patagonia, Lat. 42° 30′, (_April_.) This species, which I have taken the liberty of naming after Captain FitzRoy, the Commander of the Beagle, approaches in some respects to the _Delphinus superciliosus_ of the “Voyage de la Coquille,” but that animal does not possess the oblique dark-gray bands on the sides of the body; it likewise wants the gray mark which extends from the angle of the mouth to the pectoral fins. In the figure the under lip of the _D. superciliosus_ is represented as almost white, whereas in the present species it is black: judging from the figures, there is likewise considerable difference in the form. The figure which illustrates this description agrees with the dimensions, which were carefully taken by Mr. Darwin immediately after the animal was captured, and hence is correct. “This porpoise, which was a female, was harpooned from the Beagle in the Bay of St. Joseph, out of several, in a large troop, which were sporting round the ship. I am indebted to Captain FitzRoy for having made an excellent coloured drawing of it, when fresh killed, from which the accompanying lithograph has been taken.”—D. FAMILY—CAMELIDÆ. AUCHENIA LLAMA. _Desmarest._ Guanaco of the aborigines of Chile.