. Bulletin of the British Museum (Natural History), Geology. . Text-fig. 3. A-C. Trochiliscus {Eutrochiliscus) podolicus Corroded gyro- gonites. In B, the relation between the corroded and the normal forms is indicated diagrammatically. (A, ; C, x c. 60.) rapidly to a diameter of approximately 6011, and then expands rather suddenly to nearly three times this width: thereafter the diameter slowly decreases until the apex of the beak is reached (Text-fig. 2j). The lime-shell becomes thin where the opening reaches its greatest diameter, and the apex is often broken off along
. Bulletin of the British Museum (Natural History), Geology. . Text-fig. 3. A-C. Trochiliscus {Eutrochiliscus) podolicus Corroded gyro- gonites. In B, the relation between the corroded and the normal forms is indicated diagrammatically. (A, ; C, x c. 60.) rapidly to a diameter of approximately 6011, and then expands rather suddenly to nearly three times this width: thereafter the diameter slowly decreases until the apex of the beak is reached (Text-fig. 2j). The lime-shell becomes thin where the opening reaches its greatest diameter, and the apex is often broken off along this line of weakness. This description is supported by the examination of specimens in surface view, for the ends of the more prominent beaks are only about 100 /x across, or somewhat less, and in these the opening at the tip does not exceed a diameter of 75II. The opening is, however, considerably larger when the beak is missing. The rather variable appearances of the apical opening as shown in Text-fig. 2 may be explained by the degree of obliquity' of the sections; by more or less incomplete preservation of the beak; or by individual variations. The clear calcite of the central cavity usually extends into the narrow part of the opening, the expanded portion being filled with matrix. The corroded gyrogonites (Text-fig. 3) are, on the average, decidedly smaller. The degraded beak is often delimited from the body of the gyrogonite by a shallow groove giving the gyrogonite a rather distinctive appearance. There may also be a small, but prominent, basal projection. A few specimens with these characters have been detected in thin sections of the rock. Cf. Pia (1936: 45) on the differing appearances of random sections through short Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original British Museum (Nat
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