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Show 1890.] FROM THE WEALDEN AND PURBECK BEDS. 353 characters of the teeth is somewhat unfortunate, and this important information must be supplied before the species can be regarded as completely defined. Tbe characters enumerated above, however, are at once sufficient to exclude from comparison all known species except the typical M. macropterus, from the Lithographic Stone; and, as shown by a nearly complete specimen of the last-named form in the British Museum (no. P. 5546), it is distinguished from the Purbeck fossil by the maximum depth of the trunk being equal to the combined length of the head and trunk, while the head and opercular apparatus together occupy not less than one quarter of the total length of the fish. It is thus evident that we are concerned with a new species; and, the generic relationships of the fossil having been first recognized by Mr. William Davies (in the Brit. Mus. Register), the name of Mesodon daviesi seems appropriate. EXPLANATION OF THE PLATES. PLATE XXVIII. Fig. 1. Oligopleurus vectensis, sp. nov.; head, lateral aspect, one half natural size. Wealden; Isle of Wight. [P.M., no. 42013.] ar., articular, d.. dentary. ecpt., ectopterygoid. enpt., entopterygoid. g.r., gill-rakers, hm., hyomandibular. mpt., metapterygoid. mx., maxilla, pas., parasphenoid. pmx., premaxilla. qu., quadrate. smx., supramaxillaries. 1 a. Vertebral centrum, posterior and lateral aspects. 2. Ditto; branchial arch and gill-rakers, outer aspect. Middle Purbeck beds, Swanage. [B.M., no. P. 4219.] 3. Ditto ; first vertebral centrum of same specimen, right lateral aspect. 4. Ditto; vertebra, lateral aspect. Lbid. [B.M., no. P. 1121.] 5. Mesodon daviesi, sp. nov.; lateral aspect of fish, one half natural size. Ibid. [B.M., no. 41387.] op., operculum. P L A T E XXIX. Fig. 1. Oligopleurus vectensis, sp. nov. ; anterior portion of dentary bone, lateral aspect. Middle Purbeck beds, Swanage. [P.M., no. P. 4219.] 1 a. Tooth, enlarged four times. 2. Ditto ; preoperculum, two thirds natural size. Ibid. [University College, Bristol.] 3. Oligopleurus (? immature vectensis); lateral aspect offish, nearly natural size. Ibid. [B.M., no. 40423.] md., mandible, mtp., metapterygoid. op., operculum, p.op., preoperculum. pas., parasphenoid. qu,., quadrate. 4. Strobilodus purbeckensis, sp. nov. ; head, &c, lateral aspect. Ibid. [B.M., no. 46911.] cl., clavicle, mx., maxilla, pmx., premaxilla. p., pectoral fin. v., vertebras. Other letters as before. B.M.=British Museum. Unless otherwise stated the figs, are of the natural size. |
