Sibbaldius laticeps, _Gray_, _l. c._ p. 170, figs. 37, 38. Rudolphius laticeps, _Gray_, _Synops. Whales & Dolph._ p. 3. Balænoptera laticeps, _Van Beneden_, _Ostéogr. Cét._ t. 10 & t. 11. figs. 11-35. Inhab. North Sea. Nose of skull more than twice the length of brain-cavity from the nasal bones. 5. SIBBALDIUS. Sibbaldius, _Gray_, _l. c._ p. 175, 1865; _Synops. Whales & Dolph._ p. 3. Flowerius, _Lilljeborg_, _Nova Acta Upsal._ vi. 1867. Dorsal fin very small, far behind, and placed on a thick prominence. Ribs 14·14; first short, sternal end very broad and deeply notched. Sternum trifoliate, with a short broad hinder lobe. Scapula broad, with very long acromion and short slender coracoid process. Fingers ⸺? 1. Sibbaldius borealis. Sibbaldius borealis, _Gray_, _l. c._ p. 175, fig. 39; _Synops. Whales & Dolph._ p. 3. Flowerius gigas, _Lilljeborg_, _Nova Acta Upsal._ vi. 1867. Inhab. North Sea. Mr. Flower considers _B. borealis_, Cope, Proc. Acad. Nat. Sci. Philad. 1866, p. 297, from North Atlantic, as very nearly allied to _Balænoptera Schlegelii_. 2. Sibbaldius Schlegelii. Sibbaldius Schlegelii, _Gray_, _l. c._ p. 178, figs. 40-48; _Synops. Whales & Dolph._ p. 3. Balænoptera Schlegelii, _Van Beneden_, _Ostéogr. Cét._ t. 14 & 15. Inhab. Java. Cervical vertebræ separate (t. 14. f. 5-12); the second with a broad short lateral expansion, having a moderate-sized oblong perforation. Beak of skull very long, three and a half times the length of the brain-cavity. 3. Sibbaldius? antarcticus. Sibbaldius? antarcticus, _Gray_, _l. c._ p. 381, fig. 87; _Synops. Whales & Dolph._ p. 3. Balænoptera antarctica, _Van Beneden_, _Ostéogr. Cét._ p. 234. Inhab. Buenos Ayres. Van Beneden regards it as a doubtful species. 4. Sibbaldius sulphureus. Sibbaldius sulphureus, _Cope_, _Proc. Acad. Nat. Sci. Philad._ 1869, pp. 10, 19, f. 11. Sulphur-bottom _of the Whalers on the North-west Coast_. Dorsal fin very far back. Inhab. North Pacific, north-west coast of America, California. 5. Sibbaldius tectirostris. Sibbaldius tectirostris, _Cope_, _Proc. Acad. Nat. Sci. Philad._ 1869, p. 7. Inhab. North Pacific. Skeleton, Mus. Philad. 6. Sibbaldius tuberosus. Sibbaldius tuberosus, _Cope_, _Proc. Acad. Nat. Sci. Philad._ 1867, p. ⸺. Sibbaldius laticeps, _Cope_, _l. c._ 1866, p. 297. Inhab. North-east coast of America. Family 5. BALÆNOPTERIDÆ. _Pike Whales._ Balænopterina, _Gray_, _l. c._ p. 114. Balænoptera, _Gray_, _l. c._ p. 114; _Lilljeborg_, _Nova Acta Upsal._ vi. Balænopteridæ, _Gray_, _Synops. Whales & Dolph._ p. 3.