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Show 734 DR. J. E. GRAY ON THE CALYPTRCEIDCE. [June 27, observation that Mr. Lovell Reeve made on the remarks that I made respecting the development of the shell of Humphreyia, " That if the shell could speak it would be astonished at what was said respecting its structure." When the structure of Trochita, Crypta, Crucibulum, and Mitrella are studied in a series, it is easy to understand and to trace out how the various forms gradually pass into each other; and the peculiarity by which the genera are separated is chiefly a modification of the inner lip. And from analogy one is convinced that the curved plate at the top of the cavity of Calyptra must be a modification of the same part of the shell. As yet we have not discovered any shells which show how the modifications have been brought about, or which show any intermediate form between the plate and the cup-like appendage of Crucibulum, or the spiral lamina of Mitrella, which is most developed in Trochita. It has been suggested that it is half of the internal cup of Crucibulum: but this is a mistake; for the adductor muscle is attached to the outer surface of the cup of Crucibulum, and to the front of the inner surfaces of Calyptra; so that, if it is any modification of that cup, it must be that the two sides of the cup are compressed together, and the cuplike concavity destroyed. "We only know that the spiral shell that covers the just-hatched animal, instead of being extended in its spiral form, is developed into a nearly symmetrical conical shell without the least appearance of a spire, and that the inner lip of the nucleus is dilated into a curved subsymmetrical appendage attached to the apex of the upper part of the cavity, to the front or inner surface of which the adductor muscle which fixed the animal to the shell is affixed. As Trochita is the most spiral, and indeed exhibits the most normal form of the shell of the family, so Calyptra is the most abnormally formed shell of the group. The simple conical form of the shell and its cavity gives it some resemblance to the shell of Capulus ; and Calyptra differs from all the other genera of the family to which it is referred by the animal forming an under valve or shelly plate, as the animal of Hipponyx does among Capulida;; but the position of the adductor muscle shows that the genus, though so abnormal, is properly referred to Calyptrceidce. Tribe I. Shell conical, circular, spiral; apex central; whorls several, regular; nucleus spiral; cavity circular, spiral, with an oblong four-sided mouth. Trochitina. 1. TROCHITA, Schumacher; Adams. Trochatella, Lesson. Infundibulum, D'Orb. Shell conical, circular, spiral. Apex central. Whorls several, well developed. Base circular, concave. Mouth moderate, oblong, four-sided, transverse. Axis central, imperforated, not exposed to view. |