QUEKETT MICROSCOPICAL CLUB. 415 



living form. That which we are accustomed to find on mounted 

 slides is only a part of the organism. He was exhibiting, under a 

 microscope, a slide given him by Mr. Williams, of Folkestone, 

 which displayed very beautifully the box-like form of this diatom. 

 It consists of a top and a bottom circular plate, known as valves, 

 to each of which is attached a ring, called by some authors the 

 girdle ; that of the top or lid, as it might be called fitting 

 outside that of the lower, or box -like, part. The whole closely 

 resembles an ordinary circular " chip ' ! specimen-box. On the 

 slide exhibited, examples of an abnormal form occur, in which 

 the bottom of the box has the "girdle" greatly elongated, the 

 "lid" still remaining shallow, as in a normal form. This struc- 

 ture gives the diatom, when viewed sideways, the appearance of a 

 cylinder, instead of that of a disc with but slight depth, and when 

 observed under a binocular with dark-ground illumination the 

 difference is very striking. The girdle is marked by circles of 

 lines running round, as though it were composed of superimposed 

 rings. On the rings are small projections or points. The 

 frustules are empty, and there is no appearance of the com- 

 mencement of dividing-walls inside, which might have indicated 

 that the unusual form was owing to the beginning of the process 

 of subdivision. In a normal form the depth was 30 /x ; in a case 

 where subdivision was far advanced the depth was 54 /x. In an 

 abnormal specimen the depth was 96 /x; another was 105 /x. The 

 diameter in all the forms measured is fairly constant, varying 

 from 105 /x to 114 /x. The abnormal form is only known to occur 

 in one collection of material from Mauritius, and in that the 

 percentage is very small. No explanation or suggested cause of 

 the unusual form was forthcoming. 



Mr. Burton was complimented on the opportunity of bringing 

 this interesting slide under the notice of members. 



Several members had interesting exhibits under microscopes, 

 Mr. G. K. Dunstall showing Flosadaria cyclops, which is worthy 

 of being recorded. 



At the 499th ordinary meeting of the Club, held on May 26th, 

 1914, the President, Prof. A. Dendy, D.Sc, F.R.S., in the chair, 

 the minutes of the meeting held on April 28th were read and 

 confirmed. 



Messrs. Henry Turing Peter, Sydney G. Bills and .Robert 



