But amongst many others, I met with none more observable than this pretty Shell (described in the _Figure_ X. of the fifth _Scheme_) which, though as it was light on by chance, deserv’d to have been omitted (I being unable to direct any one to find the like) yet for its rarity was it not inconsiderable, especially upon the account of the information it may afford us. For by it we have a very good instance of the curiosity of Nature in another kind of Animals which are remov’d, by reason of their minuteness, beyond the reach of our eyes, so that as there are several sorts of Insects, as Mites, and others, so small as not yet to have had any names; (some of which I shall afterwards describe) and small Fishes, as Leeches in Vinegar; and smal vegetables, as Moss, and Rose-Leave-plants; and small Mushroms, as mould: so are there, it seems, small Shel-fish likewise, Nature shewing her curiosity in every Tribe of _Animals_, _Vegetables_, and _Minerals_. I was trying several small and single Magnifying Glasses, and casually viewing a parcel of white Sand, when I perceiv’d one of the grains exactly shap’d and wreath’d like a Shell, but endeavouring to distinguish it with my naked eye, it was so very small, that I was fain again to make use of the Glass to find it; then, whilest I thus look’d on it, with a Pin I separated all the rest of the granules of Sand, and found it afterwards to appear to the naked eye an exceeding small white spot, no bigger than the point of a Pin. Afterwards I view’d it every way with a better _Microscope_ and found it on both sides, and edge-ways, to resemble the Shell of a small Water-Snail with a flat spiral Shell: it had twelve wreathings, a, b, c, d, e, &c. all very proportionably growing one less than another toward the middle or center of the Shell, where there was a very small round white spot. I could not certainly discover whether the Shell were hollow or not, but it seem’d fill’d with somewhat, and ’tis probable that it might be _petrify’d_ as other larger Shels often are, such as are mention’d in the seventeenth _Observation_. * * * * * Observ. XII. _Of _Gravel_ in Urine._ I Have often observ’d the Sand or Gravel of Urine, which seems to be a _tartareous_ substance, generated out of a _saline_ and a _terrestrial_ substance _crystalliz’d_ together, in the form of _Tartar_, sometimes sticking to the sides of the _Urinal_, but for the most part sinking to the bottom, and there lying in the form of coorse common Sand; these, through the _Microscope_, appear to be a company of small bodies, partly transparent and partly _opacous_, some White, some Yellow, some Red, others of more brown and duskie colours.