122 PROCEEDINGS OF SOCIETIES. 



completely surrounds the axis of the embryo ; while in P. vulgaris 

 there is a considerable interval between the two halveis of the base 

 of the cotyledon, exposing the extremity of the axis of the embryo 

 or rudimentary plumule. In P. grandijlora, again, the extremtiy 

 of the cotyledon is constantly and deeply bifid, while in P. vulgaris 

 it is almost constantly entire, Dr. Dickson having only seen two 

 or at most three cases, out of a large number of embryos, where 

 the cotyledon was more or less divided at its extremity. 



Dr. John Barker showed examples of a Mallomonas (Perty), 

 probably M. Plosslii (Perty), and referred to the copy of Perty's 

 figure given in Pritchard. 



Mr. Archer ventured to think there might be two forms con- 

 founded in this genus, as the figure given by Fresenius (which 

 fortunately he happened to have brought down with him) agreed 

 much better with Dr. Barker's specimens than did Perty's figure ; 

 the latter is stouter and broader, being broadly egg-shaped, whilst 

 that of Fresenius and the present form is much narrower, and 

 might be designated as oat-shaped. 



Rev. T. Gr. Stokes exhibited some pretty and interesting Diatoms. 

 He remarked that it was very difficult to grasp the idea that the 

 genera and species of the angular forms of Diatomacese did not 

 depend upon the number of angles. He thought that at present, 

 so far as he knew, the basis of induction for this theory was rather 

 narrow, though the curious and bizarre forms of Triceratium variahUe, 

 throwing out, as they do, angles in every direction, formed a most 

 important link in the evidence. It is no small confirmation of a 

 theory if, assuming it to be true, and arguing from the seen to the 

 unseen, we are enabled to explain known or predict the discovery 

 of unknown phenomena, and that our views are justified by the 

 result. He begged to direct the attention of the meeting to what 

 he believed to be a case of this kind. In October, 18G5, the late 

 Dr. Greville published a paper in which he said that he believed 

 the Amphitetras parallela of Ehrenberg to be a quadrangular 

 form of Triceratium, although the triangular form had not yet been 

 discovered. Mr. Stokes then exhibited a specimen authenticated by 

 Dr. Greville of the quadrangular form, and a form which he (Mr. 

 Stokes) believed to be truly the triangular form of the same species. 

 Both were from the Moron deposit. Mr. Roper, of London, however, 

 thinks it to be a small form of Triceratium gigantemn. 



Mr. Stokes likewise showed a curious form which was discovered 

 by Mr. O'Meara to consist of two frustules of Biddulphia aitrita, 

 united by a perfectly transparent band of silex, leaving a fenestra-like 

 opening in the centre. 



December \9t7i, 1867. 



Mr. Archer exhibited a Difflugia which occurs in the moors 

 about Carrig and Caller}^, and yet not very commonly, but which he 

 had long noticed, and would now refer to Difflugia ohlonga (Ehr.), 

 Fresenius ; and he showed the figure given by Fresenius in his use- 

 ful paper, ' Beitrage zur Kenntniss mikroskopischer Organismen,' 



