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Biological structures lie at intersections of function, construction and history. Conversely, the geometry of structures modulates how these three aspects of organic form manifest in different taxonomic groups and ecological circumstances. Here, I apply the familiar logarithmic conispiral model for coiled shells, to assess its fit to data on gastropods, and to study covariation in coiling behavior. Treating shell centerlines as conical helices , the expansion angle of the helix, and its downward slope, or lead angle, emerge as convenient and useful parameters in studying shell growth, trait covariation, and ontogenetic allometry. I demonstrate that by combining several published datasets. Recent arguments on the inadequacy of logarithmic helicospirals contain a known methodological pitfall. Adopting the conihelical parameterization circumvents the problem altogether, demonstrating good fits of conihelical (logarithmic) centerlines to data. Further analysis of aperture inclinations, relative to conihelical centerlines, highlights the constructional developmental role of the environment (here, substrate) as a general principle of natural history, ecomorphology, and evolutionary biology, on par with adaptation. More broadly, ‘laws of form’ have practical use in data analyses and integration, and provide baseline expectations, against which observations of ontogenetic allometry, growth gradients, and other morphological features (e.g, aperture inclination, slopes of columellar folds) should be compared, to facilitate better appreciation of constructional aspects of organismal form and evolution, alongside and in relation to the adaptational and the historical.