Mr. G. J. Allman on a new genus 0/ Algae. 163 



bilis would be better removed to the new genus, as in the de- 

 scription of the species no allusion is made to the enlarged 

 globules, and as in the minuteness of the filaments as well as 

 in its general habit, it corresponds closely with the subject of 

 the present paper and with the A. ? spiralis. With respect 

 however to the right of A. impalpabilis to occupy the ground 

 assigned to it by Bory I speak with no certainty, nor would 

 my present knowledge of the plant at all justify ray meddling 

 with it. 



The only plant entirely corresponding with Bory^s genus 

 which I have had an opportunity of examining in a recent 

 state is the Anabaina membranaceu, specimens of which I ob- 

 tained in the neighbourhood of Dublin last spring. This spe- 

 cies possesses very distinctly the dilated globules ; and in the 

 large size of the filaments, and the general character and ha- 

 bit of the plant, is so completely different from the Alga of the 

 Canal Dock, that I feel certain that any one who has once 

 seen the two will not hesitate as to their complete generic 

 distinction. 



To the genus which I propose establishing for the reception 

 of the present Alga, as well as for that of Mr. Thomjjson, I 

 have given the name Trichormus : it may be characterized as 

 follows : — 



Trichormus. 

 Frond free, of indeterminate figure, consisting of simple, mi- 

 nute, moniliform, curved threads with articulations of uni- 

 form size, immersed in a gelatinous matrix. Name from 

 Opl^ hair, and 6p/j,o<; a neck/ace. 



1. T. spiralis, Thompson. Plant either diffused through the 

 water or floating on the surface ; filaments of a rich green 

 colour and regularly spiral ; when di-ied on paper of a dull 

 green without lustre. 



Colouring the water of Ballydrain lake near Belfast, Mr. 

 W. Thompson. July to October. 



2. T. incurvus, mihi. Plant either diffused through the 

 water or collected on the surface ; filaments of a pea-green 

 colour, crowded together confusedly in a gelatinous mass, va- 

 riously curved but never regularly spiral, assuming when dried 

 a fine verdigris-green colour without lustre. PI. V. 



In the Grand Canal Dock, Dublin. October. 



The difficulty experienced by naturalists in assigning to 

 many of the lower Algae their exact rank among organized 

 beings, renders any investigations into the structure and phy- 

 siological history of these doubtful organisms of peculiar in- 

 terest. So impressed was Bory Saint Vincent with a belief 

 M 2 



