A species of Graptolite, G. priodon, Bronn ([Fig. 545]), occurs plentifully in the Lower Ludlow. This fossil, referred, though somewhat doubtfully, to a form of hydrozoid or sertularian polyp, has not yet been met with in strata above the Silurian.

Star-fish, as Sir R. Murchison points out, are by no means rare in the Lower Ludlow rock. These fossils, of which six extinct genera are now known in the Ludlow series, represented by 18 species, remind us of various living forms now found in our British seas, both of the families Asteriadæ and Ophiuridæ.

Oldest known Fossil Fish.—Until 1859 there was no example of a fossil fish older than the bone-bed of the Upper Ludlow, but in that year a specimen of Pteraspis was found at Church Hill, near Leintwardine, in Shropshire, by Mr. J. E. Lee of Caerleon, F.G.S., in shale below the Aymestry limestone, associated with fossil shells of the Lower Ludlow formation—shells which differ considerably from those characterising the Upper Ludlow already described. This discovery is of no small interest as bearing on the theory of progressive development, because, according to Professor Huxley, the genus Pteraspis is allied to the sturgeon, and therefore by no means of low grade in the piscine class.

It is a fact well worthy of notice that no remains of vertebrata have yet been met with in any strata older than the Lower Ludlow.

When we reflect on the hundreds of Mollusks, Echinoderms, Trilobites, Corals, and other fossils already obtained from more ancient Silurian formations, Upper, Middle, and Lower, we may well ask whether any set of fossiliferous rocks newer in the series were ever studied with equal diligence, and over so vast an area, without yielding a single ichthyolite. Yet we must hesitate before we accept, even on such evidence, so sweeping a conclusion, as that the globe, for ages after it was inhabited by all the great classes of invertebrata, remained wholly untenanted by vertebrate animals.

Dates of the Discovery of different Classes of Fossil Vertebrata; showing the gradual progress made in tracing them to rocks of higher antiquity.

YearFormationsGeographical localities
Mammalia1798Upper EoceneParis (Gypsum of Montmartre).1
1818Lower OoliteStonesfield.2
1847Upper TriasStuttgart.3
Aves1782Upper EoceneParis (Gypsum of Montmartre).4
1839Lower EoceneIsle of Sheppey (London Clay).5
1854Lower EoceneWoolwich Beds.6
1855Lower EoceneMendon (Plastic Clay).7
1858Chloritic Series, or Upper GreensandCambridge.8
1863Upper OoliteSolenhofen.9
Reptilia1710Permian (or Zechstein)Thuringia.10
1844CarboniferousSaarbrück, nearTrèves.11
Pisces1709Permian (or Kupferschiefer)Thuringia.12
1793Carboniferous (Mountain Limestone)Glasgow.13
1828DevonianCaithness.14
1840Upper LudlowLudlow.15
1859Lower LudlowLeintwardine.16

1. George Cuvier, Bulletin Soc. Philom. xx.
2. In 1818, Cuvier, visiting the Museum of Oxford, decided on the mammalian character of a jaw from Stonesfield. See also [p. 347.]
3. Prof. Plieninger. See [p. 368.]
4. Cuvier, Ossemens Foss. Art. “Oiseaux.”
5. Prof. Owen, Geol. Trans., 2nd series, vol. vi, p. 203, 1839.
6. Upper part of the Woolwich beds. Prestwich, Quart. Geol. Journ., vol. x, p. 157.
7. Gastornis Parisiensis. Owen, Quart. Geol. Journ., vol. xii, p. 204, 1856.
8. Coprolitic bed, in the Upper Greensand. See [p. 299.]
9. The Archæopteryx macrura, Owen. See [p. 338.]
10. The fossil monitor of Thuringia (Protosaurus Speneri, V. Meyer) was figured by Spener of Berlin in 1810. (Miscel. Berlin.)
11. See [p. 406.]
12. Memorabilia Saxoniæ Subterr., Leipsic, 1709.
13. History of Rutherglen by Rev. David Ure, 1793.
14. Sedgwick and Murchison, Geol. Trans., 2nd series, vol. ii, p. 141, 1828.
15. Sir R. Murchison. See [p. 459.]
16. See [p. 461.]
Obs.—The evidence derived from foot-prints, though often to be relied on, is omitted in the above table, as being less exact than that founded on bones and teeth.

In the preceding Table a few dates are set before the reader of the discovery of different classes of animals in ancient rocks, to enable him to perceive at a glance how gradual has been our progress in tracing back the signs of vertebrata to formations of high antiquity. Such facts may be useful in warning us not to assume too hastily that the point which our retrospect may have reached at the present moment can be regarded as fixing the date of the first introduction of any one class of beings upon the earth.