204 Mr. J. Ralfs on Dickieia and Spirulina. 



XIX. — Remarks on Dickieia. By John Ralfs, Esq.* 



Dickieia, Berk. $ Ralfs. 



Frond subgelatinous, tender, plane, containing oblong scattered 

 frustules. 



In this genus the frond is so extremely tender that dried spe- 

 cimens are destroyed in the act of removing them from the paper, 

 their gelatinous matrix being apparently dissolved by the appli- 

 cation of moisture. The frond tapers at the base and expands 

 upwards into a lanceolate or obovate form. I could detect 

 neither stria? nor puncta in the frustules, which in the front view 

 are nearly quadrate, and are rarely twice as long as broad ; in 

 the lateral view they are narrow-linear with rounded ends; as 

 they do not appear to be siliceous, it is probable that dried speci- 

 mens (the only ones I have examined) become, in that view, 

 somewhat narrower than they are when recent, — a fact which I 

 have noticed in some genera of this order, whose frustules can- 

 not without injury be submitted to the action of nitric acid. 



Dickieia differs from Schizonema by its flat fronds and scat- 

 tered frustules. 



Dickieia Dansii (Thwaites) does not belong to this genus, 

 since its gelatinous matrix forms an irregular mass and not a 

 plane frond. Its frustules also differ, being decidedly siliceous, 

 striated, and having a longitudinal pellucid line and central 

 punctum (aperture, Kutzing) in the lateral view. 



1. D. ulvoides (Berk, and Ralfs). Frond undivided, obtuse at the 

 apex, Dickieia ulvoides, Berk and Ralfs, Annals of Nat. Hist, 

 vol. xiv. p. 328. t. 9 ; Kutzing, Die Kieselschaligen Bacillarien, 

 p. 119; Species Algarum, p. 109. 



Rocky shore, Aberdeen, April, Professor Dickie. 



2. D. pinnata ( ). Frond sparingly pinnate, all the divisions 



lanceolate. 



Small shallow marine pools, especially on detached masses of rock ; 

 Torquay, September, J. R. 



Fronds olive-brown, becoming greener when dried, 1 to 2 

 inches high, lanceolate, irregularly pinnated ; the pinnae lanceo- 

 late and alternate. The margins, both of the primary portion 

 and of the divisions, are uneven and minutely laciniated. The 

 frustules are like those of the preceding species. 



In 1836 I observed this plant growing plentifully near Tor- 

 quay, since which time I have had no opportunity of searching 

 for it. In the recent state it has, to the naked eye, much the 

 appearance of a minute species of Dictyota ; but it is so exceed- 



* Read before the Botanical Society of Edinburgh, May 16", 1850. 



