451 



The first of these forms resembles N. rJiomhica, figured as oc- 

 curring in the Glenshira Sand. Both forms are doubtful as to 

 genus, and may possibly prove to be Schizonemata. The second is 

 alHed to Tryblionella as well as to Nitzschia. The fifth, Pleuro- 

 sigma reversum, is a very singular form, the genus of which is not 

 quite certain. The sixth is of a genus new to Britain, and is one 

 of the forms hitherto believed to be fossil only. The next, Synedra 

 undulata, has not yet been figured entire as a British form. The 

 form which follows closely resembles it except that it has no undu- 

 lations in the margin. 



In an appendix, I have added a full description and a figure of a 

 very fine new species, detected by Professor Arnott in a gathering 

 from Teignmouth, and subsequently found, by the same observer, in 

 one from the Clyde, which justifies its introduction here. The 

 figure and description are by Dr Greville. 



The new form, Creswellia Turris, Arnott, belongs to an entirely 

 new genus, which is allied to Pyxidicula, but differs from that genus 

 as described by Ehrenberg, in forming filaments or chains. It will 

 be remembered, that I have also detected a Pyxidicula in the Clyde, 

 so that both these allied genera occur in that estuary. 



3. Short Verbal Notice of a simple and direct method of 

 Computing the Logarithm of a Number. By Edward 

 Sang, Esq. 



Mr Sang briefly explained an application of the method of con- 

 tinued fractions to the resolution of the exponential equation, and 

 illustrated it by exhibiting the computation of the logarithm of the 

 prime number 27073 directly. 



The following Donations to the Library were announced : — 



Publications of the iElfric Society, viz. — 



1. The Homilies of -^Ifric, with an English Translation. By 



Benjamin Thorpe, F.S. A. 2 vols. 8vo. — London, 1843- 

 1846. 



2. The Poetry of the Codex Vercellensis, with an English trans- 



lation. By J. M. Kemble, M.A. 8vo.— 1844-1856. 



