Chap. X.] 
FISHES OF THE LUDLOW KOCKS. 
241 
species of true Fishes identical with those of the ' Passage-beds ' is a fact of im- 
portance, as tending to connect the latter intimately with the Silurian rocks. 
Besides these, however, and in the Ludlow Bone-bed itself, there are 
remains of other Fishes * — defences of the fins of Shark-like species, with sha- 
green or skin, jaws and teeth, and other minute fragments less easily deter- 
minable. 
Onchus tenuistriatus, PI. XXXV. f. 15-17, and O. Murchisoni, f. 13, 14, are 
bony fin-spines, such as are possessed by placoid Fishes of the present day. 
Sphagodus, f. 1, 2, is the prickly skin of some such animal, and may have be- 
longed (as suggested by M'Coy) to one of the former. The small cushion-like 
bodies, f. 18, called Thelodus parvidens by Agassiz, that occur by myriads in the 
stratum, often forming large portions of its thin layers, are certainly the gra- 
nules of the skin, or shagreen, of one or other of these two common species. 
The remarkable jaws and teeth, PI. XXXV. f. 3-8, first figured in my former 
work, and named by Agassiz Plectrodus mirabilis and PI. (Sclerodus) pustuli- 
ferus (f. 9), must still be regarded as the jaws and anchylosed teeth of some 
small Ganoid fish — possibly even (as suggested by Mr. Salter) of Pteraspis or 
Cephalaspis, the teeth of these genera, if they had any, being yet unknown. 
Professor M'Coy, however, is inclined to refer these bodies also to the order of 
Crustaceans, — an opinion which, from the descriptions of Egerton, is not tenable. 
Their texture is solid and bony, and retains the jet-like lustre which the other 
fragments exhibit. 
Again, as evidence of the predaceous habits of some of these Fishes, the 
small coprolitic bodies, PI. XXXV. f. 21-28 (which, according to Dr. Pr out's 
analysis, contain the due admixture t of phosphate and carbonate of lime, with 
other matters), retain, imbedded in them, fragments of the various small 
Mollusks and Crinoids which inhabited the sea-bottom in company with 
the Fish. It thus appears that Bellerophon, Holopella, Lingula, Discina, and 
Orthis were all preyed upon by these minute but dominant creatures ; and the 
half-digested Shells remain here, as in the excrement of Fishes of many later 
formations, and of the present period, to attest the character of their food and 
the extent of their depredations. 
Thirty years have now elapsed since I announced that these Fishes of 
the Upper Ludlow rock appeared before geologists as the most ancient beings 
of their class t ; and indefatigable subsequent researches in the various 
parts of the world over which Silurian rocks extend have as yet failed 
to alter this generalization, except that one fragment of a Pteraspis 
has been found in the lower part of the same Ludlow formation (see 
p. 126). In other countries, indeed, besides our own, as in America and 
Bohemia, and notably of late in Russia, Ichthyolites have been discovered 
just within the pale of the Silurian rocks ; but there, as with us, they are 
found merely on the threshold of the system, and, except in Russia, very 
* In a survey of the May Hill district, in G-lou- land plants (one of which, seemed to be a stem, 
cestershire, made whilst the pages of the first and the others numerous seeds, termed ' spore- 
edition were passing through the press, Mr. H. cases of Lycopodiacese ' by Dr. Hooker, see p. 138) 
E. Strickland and myself, reexamining the cut- occurred in beds above the uppermost fish-layer, 
ting of the Gloucester and Eoss railroad, near and therefore at the very top of the Ludlow forma- 
Flaxley (which my friend had already described, tion, just beneath the lowest beds of the Old Eed, 
Quart. Journ, G-eol. Soc. vol. ix. p. 8), discovered in which we found a Cephalaspis, — the two depo- 
two thin bone-beds, each little more than an inch sits being there conformably juxtaposed. See 
thick, and separated by about fifteen feet of fossi- Chap. VII. 
liferous Upper Ludlow rock. On the same occa- t Sil. Syst. pp. 199, 607. 
sion we observed that the only remains of small I Sil. Syst. ch. 45, p. 605. 
K 
