A large suite of specimens belonging to the Early Bajocian Stephanoceras from Évrecy (Normandy, France) displays wide variation in conch and sculpture. The quantitative analysis of the conch geometry and its ontogeny on the basis of more than 50 sectioned specimens reveals major problems in the separation of species within the assemblage; clear morphological boundaries between possible species cannot be established. The material shows wide variation in sculpture and conch parameters throughout ontogeny, and correlation between the characters is weak. With the study of conch ontogeny, it is possible to separate dimorphs, as microconchs show a sudden change in the conch parameters (umbilical egression, change in the shape of the whorl profile). The onset of these changes varies in the assemblage between 40 and 75 mm conch diameter.

中文翻译：

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来自法国诺曼底的早期 Bajocian 菊石 Stephanoceras 的海螺几何、个体发育和二态性

属于早期 Bajocian Stephanoceras的一大套标本来自Évrecy（法国诺曼底）的海螺和雕塑展示了广泛的变化。基于 50 多个切片标本的海螺几何形状及其个体发育的定量分析揭示了组合内物种分离的主要问题；无法在可能的物种之间建立明确的形态界限。该材料在整个个体发育过程中表现出雕塑和海螺参数的广泛变化，并且字符之间的相关性较弱。通过对海螺个体发育的研究，可以分离二形体，因为微型海螺表现出海螺参数的突然变化（脐排出，螺纹轮廓形状的变化）。这些变化的开始在 40 到 75 毫米海螺直径之间的组合中有所不同。