212 PROCEEDINGS OF THE COTTESWOLD CLUB 



is necessary to use an achromatic condenser with an 

 angular aperture, adjusted for the angle of the objective, 

 and verv carefully centred. The coccoliths are of various 

 forms, mostly consisting of an elliptical ring, either plain 

 or marked by transverse lines, giving the ring a jointed 

 appearance ; and in many cases the space inside the ring is 

 occupied by a granular film. Ehrenberg, Huxley, Wallich, 

 and others have theorised about these organisms ; but by a 

 later authority they are believed to belong to the Algae. 

 The best method (at least, according to my own experience) 

 to obtain coccoliths for mounting is to take a small 

 quantity of whiting, well mix it up with water to the 

 consistency of cream, and then let it stand in a small 

 beaker or large test tube until the heavier portions of the 

 whiting have settled, leaving the water at the top apparently 

 clear. Upon the surface of the water will be found a kind 

 of scum, which should be avoided. With a rather fine- 

 pointed pipette take up some of the water, taking care not 

 to disturb the sediment ; put a cork in the upper end of 

 the pipette, and stand it, with the open point downwards, 

 upon a clean cover glass, upon which a drop of distilled 

 water has been placed. After about a quarter of an hour 

 the coccoliths will have settled to the bottom, and will be 

 found in the drop of distilled water. This drop should 

 be spread evenly over the covering glass, evaporated very 

 slowly, the residue moistened with benzole or turpentine, 

 and mounted in pure Canada balsam. 



Diatoms of several kinds are present in chalk — not 

 abundantly, I beheve ; but still they are to be found. I 

 have never searched specially for these organisms, and 

 cannot say how many genera and species occur. Two 

 species of Fragillaria are mentioned in the Micrographic 

 Dictionary as having been found by Ehrenberg; and Dr. 

 Carpenter figures a Navicula in his work on the micro- 

 scope. Upon a slide which I mounted for coccoliths 



