Mr. S. V. Wood's Catalogue of Shells fr'om the Crag. 455 each other, and hence much of the secondary layer is not re-solvable into distinct fibres. At certain places, however, slight variations in the curves take place ; they become opposed, and a small depression of the outer membrane results, or the few opposed curves may be large, and hence a greater hollow will ensue ; but in these vessels very little matter is added to the internal layer, perhaps hone, and hence no dot or canal is ap-parent in them (PI. XII. fig. d.). The spiral and sinuous direction of the fibres of the se-condary layer is very easily recognizable, at least when punc-tated vessels are carefully examined ; but the attention of the observer should be strongly directed to it, as the brighter ap-pearance of the punctations themselves, from the light only passing through a less thickened layer of membrane, draws more powerful consideration to them. It may also be well observed when a vessel is cut, or when it breaks itself at the side (as at fig./l). The section of a completely formed punctation is seen at PI. XII. fig. ^; the dotted line indicates the primary mem-brane, the broader dark line beneath it the fibre. It will be seen that we thus differ from Mohl in believing that a secondarily formed fibrous layer, consisting of fila-ments bent upon themselves, is mainly instrumental in the formation of puiictations, and agree with him in the circum-stance of the depression being caused by a sinking-in of the primary membrane, but which latter condition never could exist without the previous existence of the fibres alluded to. We also consider the fibres or filaments not to be of primary development, and not as serving in this particular as a sup-port to Dr. Barry, in what we have thought to have been his views. (Figs, a, and b, are from Meyen.) XLIX. — A Catalogue of Shells from the Crag, By S. V. Wood, Esq., F.G.S. [With a Plate.] [Continued from vol. vi. p. 253.] To the Editors of the Annals of Natural History. Gentlemen, It has been my object with the present as well as the prece-ding portion of this Catalogue to adhere as closely as possible to the classification of Lamarck ; my only deviations from the system of that eminent naturalist are those rendered necessary by the additions that have been made to the science of Mala-cology, and the establishment of new genera by other writers. I have also myself thought it requisite to propose a few for
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