326 philosophk:al tbansactions. [anno 1747. 



This specimen, shown to the Society, was about 12 inches long, 5 inches 

 broad, and in some places near 2 inches thick; rough on the under side, as 

 though broken off from the rock it had been affixed to; and the upper side was 

 composed of smooth polished knobs, in form like the botryoid iron ore. 



Sir Hans Sloane, in his noble museum, had several specimens of these ori- 

 ental turquoises, all botryoid; especially a mass from China, about 3 inches 

 long, 2 broad, and near an inch thick; all which seem to be copper ores; and 

 he had likewise samples of turquoises from Spain, and the south of France; 

 which were all small, and seemed really to be pieces of ivory tinged with copper. 



Of a Curtails Echinites. By Mr. Henry Baker, F. R. S. N° 482, p. 432. 



Mr. Baker showed the Society a very extraordinary echinites, the like to which 

 he had never seen in any museum, or found described by any author. For the 

 echinitae usually met with, are made up either of chalk or flint, or some stony, 

 chalky, or sparry matter, formed within the shell of the echinites, and thence 

 taking their figure as in a mould : which shell is often broken off and gone, but 

 at other times remains impregnated with talcy or sparry particles; whereas the 

 present subject is composed of a transparent crystalline substance, which has re- 

 ceived its general figure by having been circumscribed within the shell of some 

 echinus, and shows linear ridges and divisions correspondent to the lines and 

 plates found in this kind of echinus. 



Were this all, it would be a very uncommon production, as these bodies have 

 been very rarely known to be formed of crystal;* but it is rendered much more 

 curious and extraordinary by having pxact rows and series of little cells, all of 

 the same regular figure, though lessening gradually in size, as they ascend from 

 the base upwards. See fig. 5, pi. 7 . 



This body having been formed within the shell of an echinus, one would ex- 

 pect, as is the case in all other echinitae usually known, that its figure should be 

 exactly answerable to the mould in which it was formed; but Mr. Baker observes, 

 that the echinus's shell is perfectly smooth internally, having no rising parts cor- 

 respondent to these cells or cavities; and therefore, as it could not receive its 

 configuration from thence, it must be owing to the natural shooting of the crys- ' 

 talline matter, or to some other cause, which he does not pretend to know.-f- 



The configuration seems however in some measure to correspond with the 

 nature of the shell in which it was formed ; as to the number of the rows of 

 cells, these being ranged by fives, as the papillae, indentings, lines, or other 

 marks on the recent shells of echini constantly are; these rows are 20 in number, 



• Sir Hans Sloane had a mass, which was formed within an echinus, the shell being broken off; 

 it was one half or side crystal, the other side of a substance like chalk, but much harder. — Orig. 

 + Perhaps to some cells or membranes belonging to the body of the echinus. C. M.— Orig. 



