valves only, and to float free, with, perhaps, some voluntary impulse), it arrives at the vacant hole of some small Petricola, Lithodonirs, or other perforating Testacean which suits it, one valve soon becomes attached to the wall of the hole, and then the animal proceeds to secrete the siphonic sheath or tube, to enlarge the chamber according to its necessities, and to form the Shelly perforated tubular plate which is to give admission to the water at the practicable part of the chamber. How the excavation is carried on 15 also doubtfuL The chambers of the individuals of Clavagella australia, described by Mr. Broderip, were formed in a siliceous grit, those of C. dongata in an Astrceopore, that of C. later in a calcareous grit, and those of C. Melitensis in an argillo-calcareous tufa. " If,' says the author last mentioned, "the excavation be the work of a solvent secretion, it must be a solvent of extensive power. The situation of the glands, detected by my friend Mr. Owen, leads me to think that they minister in some way to this operation ; and I do not see how the anterior or greater end of the chamber can be operated on by mere mechanical attrition with such parts as must have been contiguous to it. It has been objected that any solvent which would act on a calcareous rock would equally act on the calcareous shell of the animal ; but there is perhaps more of point than of strength in this objection. Without laying too much stress on that law of nature by which chemical and vital forces are placed in a state of hostility, and which may or may not be applicable to such a substance as shell, the gland for the secretion of the supposed solvent, as well as the organ for applying it, may be so placed as that the solvent shall only come in contact with the inorganic or dead substance to be acted on without touching the shell. Again, it has been asked, what solvent would act equally on a calcareous and on a siliceous sub stance ? To this it may be answered, first, that it is not pretended that the nature of the supposed solvent is known; secondly, that in siliceous grits, there is more or less calcareous matter by which the mass is held together, and that the solution of the calcareous particles would be followed by the disintegration of the stone One observation, arising from the various depths at which the recent species have been found, will not, perhaps, be deemed irrelevant. C. australis was so near the surface at low water, that it was detected by its ejection of the fluid ; C. elongate, from the nature of the coral in which it was chambered, could not have been living far beneath the surface ; whereas a late was dredged up from a depth of 66 feet. Any inferences, therefore, as to the state of submersion of a rock during the life of the fossil species of Claragella which there occur, should be made with caution by the geologist."
The geographical distribution of the genus, though now compara tively rare in cabinets, is probably wide. A sharp investigation of masses of coral and of submerged perforated rocks or stones, particu larly in warm climates, is very likely to be rewarded by the discovery of Clavagella.
With regard to its place amongst the other Mollusca, Professor Owen is of opinion that the organisation of Clavagella, like that of Aspergillum described in the Heise von Afrik' of Dr. Rtippell, is modelled on the type of the Acephalous Bivalves; and that it follows most closely, in the variations from that type, the modifications which have been observed in Gastrochcsna. The lengthened worm-like figure of Aspergillum is exchanged in Claragella, observes Professor Owen, for a shorter form with greater lateral development ; and instead of the small rudimentary valves, which are enchased, as it were, in the calcareous sheath of A spergillunt, we find them here largely developed, and one of them always remaining at liberty, to be applied by a powerful muscular apparatus to those offices which are essential to the forcible expulsion of the fluid in the branchial cavity, and pro bably to assist in the excavation of its secure abode.
Fossil Claregdlcs.
Mr. Broderip says that no fossil species appear to have been detected below the Supracretaceous group. M. Deshayes, in his tables, gives two living and seven fossil (tertiary) species, and one (C. aperta, Sowerby) as found both living and fossil (tertiary). He gives the Mediterranean and Indian Ocean as the habitation of the living animal, and Sicily (Pliocene Period of Lyell) as the locality of the fossil. In his edition of Lamarek lie makes the whole number (living and fossil) seven, the seventh and last species being C. aperta ; but he refers to Rang's 'Manuel' for a second living species. a coronata is found in the London Clay. In Deshayes's edition of Lamarck, the species C. eehinata is followed by a eristata ; and the editor, in a note referred to from the latter, says that these two species should be united, as they only differ in size and age. He also observes that the free valve of a cristata, or of C. tibialis, has been placed by Lamarck among the species of Glycimeris under the name of G. mar garitacea. And here we may mention the difficulty of laying down specific characters from the valves, which being, as Mr. Broderip remarks, nearly, perhaps altogether, excluded from the light, colour, at best but a treacherous guide, is absent entirely ; while the shape of the chamber and of the valves, together with the comparative roughness or smoothness of their outer surfaces, may depend upon the greater or less degree of hardness of the material in which the chamber is formed,