735 



APPENDIX. 



Mr J. J. Lister, F.R.S., has favoured me with the following additional note, "On the 

 mineralogical character of the skeleton of Astrosclera," which he has received from Mr Hutchinson 

 of Pembroke College, Cambridge. 



" A short time after the publication of the description of the mineralogical characters 

 of the skeleton of Astrosclera willeyana, an important paper was communicated to the 

 Mineralogical Society by Miss Agnes Kelly, entitled "Conchite, a new form of Calcium 

 Carbonate" (Min. Mag., Vol. xn. p. 363, 1900). In this paper the authoress claims to 

 have established the existence of a form of calcium carbonate distinct from calcite and from 

 aragonite, and to have shown that all calcium carbonate of organic origin, formerly believed 

 to be aragonite, really belongs to the new variety. 



"The specific gravity of conchite is given as 2-830 — 2-865. It is uniaxial and negative. 

 Its birefringence is less than that of calcite, and the maximum value obtained for its index 

 of refraction w D = 1-661 is less than either /? or y of aragonite. 



"Miss Kelly's conclusions have however been questioned by Brauns (Centralbl. fur Min., 

 1901, 134) and by Vater (Zeit. fur Kryst., xxxv. 166), who maintain that conchite is essentially 

 the same as aragonite. 



"Meigen (Centralbl. fur Min., 1901, 577) has recently shown that aragonite and calcite 

 in fine powder behave differently when boiled with cobalt nitrate solution, the former turning 

 reddish-lilac, while the latter remains white or becomes yellowish. G. Panebianco (Rivista 

 Min. Ital., xxviii. 5 — 12) confirms Meigen's observations as regards aragonite but finds 

 that calcite turns sky-blue. Astrosclera when submitted to this test gives the colour 

 characteristic of aragonite. The conclusion drawn from the specific gravity determination, 

 that the skeleton of Astrosclera is not calcite, is thus satisfactorily confirmed. Its properties 

 as given in my previous description agree with those of conchite, but until the independence 

 of conchite and aragonite is more definitely established, the mineral element present in 

 Astrosclera may best be regarded as aragonite. 



A HUTCHINSON." 



