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Show 408 DR. GWYN JEFFREYS ON MOLLUSCA OF THE [Apr. 16, Mus. Comp. Zool. No. 7,1869, p. 127), " Very young specimens are flatter, rounded, and have a strait margin; they could scarcely be distinguished from the young of Terebratula cubensis, if it was not for the loop and septum seen by transparency. There is also some variety of form in the old; in some specimens the length is greater than the breadth, and there is considerable diversity in the sinuosity of the frontal margin." T. septata is not less variable in shape and in the flexuosity of the front margin ; a young specimen which I dredged in the ' Porcupine ' Expedition of 1870, attached to a branch of Oculina prolifera, was mistaken by me for Terebratella spitzber-gensis, having the same oval and laterally compressed outline, and a similar septum visible through the shell. In young and half-grown specimens of T. septata, as well as in other allied species, the side flanges or flaps of the loop are closed by a membrane, which is removable; the openings then appear. The inner layer of the shell is microscopically and closely striated lengthwise. The gradual development of the skeleton or apophy-sary process, indicated by the changes which take place in the course of growth, is very remarkable, and is shown in the accompanying figures (Plate XXIII. figs. 1 a, b, c). Mr. Davidson and I agree that the loop in T. septata, when quite young, resembles that of a Megerlia, and is three times attached ; at a rather more advanced age it assumes the form of a Terebratella, and is twice attached; in the full-grown state it has all the characteristics of the subgenus Waldheimia, and is attached only to the hinge-plate. Mr. Friele has also, to some extent, demonstrated these retrograde changes in his papers above referred to. This species is unquestionably the T. septigera of Loven (1846), and equally without doubt (so far as m y opinion is worth any thing in either case) the T. septata of Philippi, 1844. Seguenza, however, considers Philippi's species to belong to the genus Terebratella ; and he has named Loven's species Waldheimia peloritana. Although the skeleton represented in Philippi's figure was imperfect, there is no appearance of the cross bar to which the loop is attached in Terebratella, and which cross bar is not less persistent than the septum in broken and worn specimens of so many species of that genus as well as of Megerlia. Indeed his description and figures agree as closely with imperfect specimens of T. septigera, as those of his T. euthyra with imperfect specimens of T. cranium. Seguenza may have found in the Sicilian Tertiaries not only his W. peloritana, which he now refers to T. septigera, but also a species of Terebratella which he regards as Philippi's species. For this last-mentioned species, if not known in a recent or living state, he might give another name. Were not priority of publication an essential standpoint for scientific nomenclature, septigera might be retained for the recent species, and septata for Seguenza's fossil species of Terebratella ; but in the absence of better data it may be more advisable " quieta non moveri." W. peloritana and W.fioridana appear to be the same variety of T. septata. I cannot refrain from expressing my admiration of the careful and |
