Mr. Miller dissected specimens of every genus, and has figured the separate plates or bones that enter into the composition of the receptacle,[302] and arms. Traces of the tentacula, and their subdivisions, must be sought for, and if discovered, should be removed with the stone to which they are attached, and the block be afterwards reduced in size by a mason's saw, and not by the blows of a hammer, which might displace the ossicula.
[302] Natural History of the Crinoidea.
If imbedded in Lias shale, or other fragile material, a thick slab should be removed, for greater safety in conveyance; this, when reduced to a convenient size and thinness, may be imbedded in a tray with plaster of Paris, or glued to a piece of thin, well-seasoned mahogany, or deal. The specimens of the Pear Encrinite of Bradford, and of the Pentacrinites from Lyme Regis, in the British Museum,[303] were prepared in this manner.
[303] Petrifactions, p. 78.
The crinoideal remains in Chalk belong but to few genera; they merely require the usual manipulation of cretaceous fossils. The collector, however, should remember that the ossicula and plates of the receptacle (as for instance of the Marsupites), are but slightly adherent to each other, and the chalk must not be wholly removed, or these parts will become detached.
The receptacles of the Apiocrinites of the chalk are rarely found with more than a few joints of the column attached; and I believe no vestiges of the arms have been observed: these parts are therefore desiderata, and should be diligently sought for: the radicles of these crinoideans are long, articulated, and branching, and without due caution may be mistaken for the arms, or for another species. The first remark will also apply to the Marsupite; any specimens with but a few ossicula of the arms are very precious. I may observe that there is yet much to learn as to the number of species and genera, and the peculiar characters of the Crinoidea of the chalk, and that any addition to our knowledge on this subject will be valuable.
The Asteridæ are so simple in form and structure, that it is unnecessary to offer any suggestions for their development; of course they must not be removed from the stone.
Among the detached ossicula dispersed through the chalk, the student will remember that the large madrepore-like tubercle of the Star-fishes, (ante, [p. 304].,) may often occur. It may easily be mistaken for an encrinital body, or for a coral, but an accurate inspection will show that it is not composed of anchylosed plates, like the receptacle of an Apiocrinite, but has surfaces for attachment to other ossicula; while the ends, which in a crinoideal column would have radiated surfaces, are rounded and entire.
In collecting Echinites, much caution is required in dissecting specimens surrounded by spines. If imbedded in hard limestone, or in laminated clay, it is scarcely possible to preserve the spines in connexion with the shell; but it often happens that the Cidarites of the Oolite are attached by the base to the solid limestone, and the case with the spines is imbedded in sandy, friable aggregate, not difficult of removal. A specimen in my cabinet, with upwards of fifty spines attached to the shell, was obtained under such circumstances.[304]
[304] Now in the British Museum.