406 Mr. T. Austin on the genus Dunstervillia. 



teeth in D. Swartzii have two angles, whereas they arc rounded 

 in the present plant. 



As there are three sides in one plant and four in the other, 

 whilst the sides in both are equal, the filament of D. quadrangu- 

 latum is stouter ; for the same reason, instead of one dark longi- 

 tudinal line it has two lines running from side to side and cross- 

 ing each other : the additional line of course depends on the ad- 

 ditional angle. When these lines approach the opposite margins 

 of the filament only one side is presented to the eye, and the fila- 

 ment is then of the same breadth as in D. Swartzii, but as it is 

 regularly twisted its apparent breadth varies, being greatest where 

 the two dark lines cross each other in the middle. The end view 

 also has one more angle, and therefore the endochrome exhibits 

 four instead of three rays. 



I must confess that I am inclined to agree with Mr. Berkeley 

 and Mr. Borrer, and to regard it as a variety of Desmidium 

 Swartzii ; but as I have gathered it for two succeeding years 

 quite unmixed with that species, and as Mr. Berkeley well ob- 

 serves (in a letter), that "whether considered as a species or va- 

 riety it is a remarkable plant and well-deserving of notice," I have 

 preferred to describe it as distinct. 



Plate XII. fig. 9. Desmidium quadrangulatum. 



[The following paragraphs, which should have been inserted in 

 the description oi Xanthidium furcatum at p. 466 of the previous 

 volume, were omitted by accident.] 



Near the centre of each segment there is a curious projection 

 on each surface. In the front view, and especially before the 

 escape of the endochrome, these projections are liable to be over- 

 looked, and even in the empty fronds some attention is requisite 

 for their discovery. 



The best method of detecting them is to adjust the microscope 

 for a view of the frond, and then gradually to raise the lens ; as 

 soon as the frond becomes slightly indistinct, the projections will 

 be rendered visible. In this aspect they are circular with mar- 

 ginal teeth, somewhat resembling the peristome of a moss. In 

 a lateral view the processes are more distinct, rather broader than 

 high, and dentate at the end. 



LVIII. — Note on Mr. BowerbanVs Paper on the genus Dunster- 

 villia [Bowerhank), with Remarks on the Ischadites Konigii, the 

 Tentaculites and the Conularia. By Thomas Austin, Esq., 

 F.G.S. 

 When reading in the ^ Annals ' for the present month Mr. Bower- 

 banVs very interesting observations on a new genus of calcareous 



