covered by a thick coating of lithic, which is occasionally broken by a layer of the triple crystals, and the external surface is principally composed of the fusible Calculus.-Its present weight, after being sawn, is 32 oz. 7 dr.; the specific gravity 1.756, which after being two days in water became 1.768.-It measures 15 inches in circumference in one direction, and 13 inches in the other.

The largest Calculus in this kingdom, is, I believe, that which is described in the Philosophical Transactions for 1809, which weighs 44 oz.; but it is composed entirely of the phosphates, and, from its structure, seems rather a number of calculi cemented together, than one formed, in the usual manner by concentric layers. In the description of this Calculus by Sir J. Earle, is given a quotation from Fourcroy, of which it afforded a confirmation, that all the very large Calculi are composed of the Phosphates.The Calculus which is the subject of this paper, is a remarkable exception to the general rule, as nine-tenths of it at least are lithic.

I have been induced to give this brief notice of it to this Society, that, if you think it worth publication, so interesting a specimen may be withdrawn from the obscurity in which it has lain for upwards of a century.

As an appendix to this paper I request your attention to another, and in some respects a similar specimen, presented to me for examination by Dr. Thackeray.

It is a concretion formed in the intestines of a horse, weighing upwards of 64 oz., and measuring 37 inches in the largest circumference, and 26 in the least. Its composition, as might be expected, is principally of vegetable matter, but mixed with a considerable portion of the phosphates.

Its enormous size makes it a subject for curiosity, though fortunately, the absence of such concretions from the human frame, divests it of the painful interest we cannot but feel in the former specimen.

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DESCRIPTION OF THE PLATE.

Fig. 1. Exterior of the Calculus; the size of the Original.
A. B. The line of section.

Fig. 2. Section of the Calculus.