Fig. 97.—The Common Dolphin (Delphinus delphis). From Reinhardt.
Tursiops.[169]—Rostrum tapering moderately from base to apex; palate not grooved; symphysis of mandible short; other cranial characters as in Delphinus. Teeth ²¹⁄₂₁ to ²⁵⁄₂₅, stout (6 to 7 mm. in antero-posterior diameter). Vertebræ: C 7, D 13, L 17, C 27; total 64. Limbs as in Delphinus. Represented by the widely distributed T. tursio; T. catalania being a second form. Fossil remains of this genus from the Italian Pliocene have been recently described.
Prodelphinus.[170]—Rostrum somewhat variable; mandibular symphysis short (less than one-fifth the length of the ramus); other cranial characters as in the preceding genus. Teeth ³⁰⁄₃₀ to ⁵⁰⁄₅₀, small, not exceeding 3 mm. in diameter. Vertebræ 73 to 78. Limbs as in Delphinus. Four leading types of this genus are recognised (all of which have numerous synonyms) viz. P. obscurus, P. euphrosyne, P. doris, and P. longirostris.
Péron’s Dolphin (Delphinus leucorhamphus, Péron, or Leucorhamphus peroni, Lilljeborg) resembles some forms of Prodelphinus in its cranial characters; but having no dorsal fin, it has been separated generically by some writers. It is not improbable that Delphinus borealis, Peale, from the North Pacific, in which there is likewise no dorsal fin, may be an allied form.
Steno.[171]—Rostrum long, narrow, and compressed, very distinct from the cranium; mandibular symphysis as long as, or longer than one-fourth the length of the ramus; other cranial characters as in the preceding genus. Teeth ²¹⁄₂₁ to ²⁵⁄₂₅, of comparatively large size (5-6 mm. in diameter); surface of their crowns finely grooved. Vertebræ: C 7, D 12, L 15, C 32; total 66. Represented by S. rostratus, from which the forms which have received other names are probably not specifically separable.
Sotalia.[172]—Pterygoids narrow, not meeting in the middle line, and in their inner borders diverging posteriorly, instead of being parallel as in the preceding genera; other cranial characters much as in Steno. Teeth tolerably large (4-5 mm. in diameter), ³⁰⁄₃₀ to ³⁵⁄₃₅, with smooth enamelled surface. Vertebræ: C 7, D 12, L 10-14, C 22; total 51-55. Pectoral fin broad at base, the breadth being caused by the considerable development and position of the two outer digits. Six species are provisionally recognised as distinct, including the Chinese White Dolphin (S. sinensis) and S. pallidus from the river Amazon.
Bibliography of Cetacea.—D. F. Eschricht, Untersuchungen über die Nordischen Wallthiere, 1849, contains a copious bibliography of the group up to the date of publication. Since that time numerous monographs on special families and genera have been published, and a large illustrated general work, Ostéographie des Cétacés, by P. J. Van Beneden and P. Gervais, 1869-80. Besides those already referred to in the footnotes, the following may be mentioned; viz. J. F. Brandt, “Untersuchungen über die Fossilen und Subfossilen Cetaceen Europa’s,” in Mém. de l’Acad. Imp. de St. Pétersbourg, 7ⁱᵉᵐᵉ sér. vol. xx. 1873; C. M. Scammon, Marine Mammals of the N. W. Coast of North America, 1874; W. H. Flower, “On the characters and Divisions of the Families of the Delphinidæ,” Proc. Zool. Soc. 1883, p. 466, and List of the Specimens of Cetacea in the British Museum, 1885; F. W. True, “Review of the Family Delphinidæ,” Bull. U.S. Nat. Museum, No. 36, 1889; P. J. Van Beneden, Histoire Naturelle des Cétacés des Mers d’Europe, 1889.
For fossil forms, in addition to the works of Van Beneden, Gervais, and Brandt, already cited, the reader may refer to various memoirs published by the former writer in the Bull. Ac. R. Belgique and Ann. Mus. R. Hist. Nat. Belg. See also R. Lydekker, “The Cetacea of the Suffolk Crag,” Quart. Journ. Geol. Soc. vol. xlii. p. 7 (1887), and Catalogue of the Fossil Mammalia in the British Museum, pt. v. (1887).