PROCEEDINGS OF THE SOCIETY. 617 



being from l-2000tli to l-lOOOth in. Each consists of about 24 

 rays united centrally by simple contact, and not by any visible medium, 

 and free peripherally and at their sides. Each ray is longer than 

 broad, pointed externally rather bluntly, and less so towards the 

 centre of the star. The shape is that of a blunt scalenohedron, and 

 as the free terminations project as the ends of radii on all sides, the 

 mineral not being very transparent and its faces being highly refrac- 

 tive, the stars are by no means easy to define. 



Under a power of 200, with a black spot lens beneath, the appear- 

 ance presented is very beautiful ; and a still higher power, with the 

 careful employment of the achromatic condenser and diaphragm, 

 shows the outlines of the crystals very distinctly. Here and there a 

 star may be seen to be incomplete, and two or three rays only may be 

 in apposition by their thicker end. The shape of the ray is then 

 observed to resemble a long obliquely placed rhombohedric crystal of 

 calcite. Polarized light developes an object of great beauty, each ray 

 showing a play of colours as the Nicol is revolved, but not developing 

 a definite cross. 



In some specimens, layer on layer of the stellates exists, and 

 foreign objects such as half-dissolved siliceous sponge-spicules may be 

 intermixed. 



No trace of organization can be seen in the thin basal film. 



That these stellates are of calcic carbonate there is little doubt ; 

 and from what can be made out, I do not feel disposed to connect 

 them with any organism with which I am acquainted. I therefore 

 seek for information at the hands of any of the Fellows." 



Mr. Stewart thought from the description given by the President, 

 as well as from looking at the specimens exhibited under the Micro- 

 scope in the room, that the objects referred to were not spicules but 

 rather modified groups of crystals such as were found in the bodies of 

 some of the Ascidians. On examining a portion of a large mass of 

 crystals by polarized light it would be found that each one of the 

 processes had its own special optic axis which corresponded with the 

 optic axis of the crystallized body, whereas in the case of the ordinary 

 spicule this was not so, but rather as if the spicule was carved out 

 of a piece of calcite. He thought those which the President had 

 described were probably derived from a species of Botrillus which 

 formed an extremely thin film over various bodies, and when dried up 

 had the appearance of a portion of a visiting card of extreme white- 

 ness, the whiteness being due almost entirely to the groups of these 

 crystals. 



Prof. F. Jeffrey Bell read his paper " On the Spicules of Cucu- 

 maria hyndmanni, G. calcigera, and two allied forms " (p. 481). 



The President said that if any one wanted to work at this subject, 

 materials were very easy to obtain, and he should be very glad to 

 supply some sea-cucumbers to begin with, which had been sent to him 

 some time ago, but which he had almost thought of returning for want 

 of time to devote to them. 



Ser. 2.— Vol. III. 2 S 



