Geology and Mineralogy considered with reference to Natural Theology/Plate 27d

From Wikisource
Jump to navigation Jump to search
Geology and Mineralogy considered with reference to Natural Theology, plate 27d.png

Plate 27d. V. I. p. 218, Note.

A. Teeth of a recent Shark, allied to fossil species.
Fig. 1. Anterior and Palatal Teeth of the Port Jackson Shark, (Cestracion Phillippi.) (Phillip.)
Fig. 2. Anterior cutting teeth of Port Jackson Shark, in the College of Surgeons, London. (Owen.)
Fig. 3. Flat tessellated tooth of the same. Nat. size. a. Outer articular facet, showing the tubular structure of the bony base. b. Punctate surface of the superficial enamel. (Owen.)
Fig. 4. Mesial, and inner articular facet of another large tooth of the same. a. Upper concave margin thinly covered with enamel, b. Lower bony margin without enamel, a, b. Bony base of the tooth exposed by removal of the Enamel. The surface is areolar, from the bending and blending together of the bony tubes, c, c'. Fractured edge of the marginal and superficial enamel. (Owen.)
Fig. 5. Another anterior cutting tooth, a. Smooth enamelled point, b. Minutely rugous and tuberculated base. In some of the cutting teeth both sides of the base are rugous. (Owen.)
B. Various forms of fossil Teeth, in the three sub-families of Sharks. (B. 1. to B. 13. Agassiz.)
Figs. 1—5. Teeth of fossil Sharks in the sub-family of Cestracionts. See V. I. p. 218.
Fig. 1. Psammodus, from Mountain limestone, Bristol.
Fig. 2. Orodus, from the same.
Fig. 3. Acrodus, from the Lias, Lyme Regis.
Fig. 4. Ptychodus, (upper surface) from the Chalk.
Fig. 5. Side View of fig. 4.
Figs. 6—10. Teeth of extinct fossil Sharks in the subfamily of Hybodonts; in this family the enamel is plicated on both sides of the teeth. See V. I. p. 219, Note.
Fig. 6. Side view of tooth of Onchus, from the Lias at Lyme Regis.
Fig. 7. Front view of the same.
Figs. 8. 9. 10. Teeth of Hybodonts, from the Oolitic slate of Stonesfield, Oxon.
Figs. 11. 12. 13. Fossil Teeth of true Sharks in the Squaloid division of that family, having the Enamel smooth on the outer side. From the Chalk and London clay. See V. I. p. 220, Note.
Fig. 14. Palatal teeth of Myliobates striatus, from the London clay of Barton cliff, Hants. See V. I. p. 221. Much of the enamel is worn away by use, as frequently happens in the tongue and palatal bones of living Rays. (Original.)
C. Petrified remains of an extinct Genus of Shark.
Fig. 1. Jaw of Hybodus reticulatus, from the Lias at Lyme Regis, (scale one half.) Many of the Teeth retain their place on the margin of the bone. The granulated structure of bone is distinctly preserved. (De la Beche.)
Fig. 2. Teeth selected from the Jaw last figured. Nat. size.
Fig. 3. Ichthyodorulite, from the Lias at Lyme Regis, being the Dorsal spine of Hybodus incurvus, set with teeth-like hooks, to suspend the membrane of the dorsal fin. (De la Beche.)

A double row of similar hooks occurs on the first dorsal ray of the Barbel, (Barbus Vulgaris.) And on the anterior ray both of the dorsal and anal fins of the Carp, (Cyprinus Carpio.)

Fig. 4. Transverse Section of fig. 3, at a.[1] (De la Beche.)

  1. In the Lond. and Edin. Phil. Mag. Jan. 1836, the author has published a notice of his recent discovery of the jaws of four extinct species of fossil fishes of the genus Chimæra, a genus hitherto unknown in a fossil state. The only known species (C. monstrosa) approximates most nearly to the family of Sharks; and is found pursuing Herrings and other migratory fishes. The Chimæra is one of the most remarkable among living fishes, as a link in the family of Chondropterygians; and the discovery of a similar link, in the geological epochs of the Oolitic and Cretaceous formations, shows that the duration of this curious genus has extended through a greater range of geological epochs, than that of any other genus of fishes yet ascertained by Professor Agassiz, and leads to important considerations in Physiology.

    The Chimæra partakes of one remarkable character with the Cestracion Phillippi, whereby this species alone, among living Sharks, is connected with the extinct forms of that family, in having the first ray of the dorsal fin enlarged into a strong bony spine armed with sharp hooks, like the Ichthyodorulite of the earliest fossil Sharks.