pinnated with slender, obliquely inserted veins, which proceed to the mar- 

 gin, and are excurrent into marginal, toothlike, cloven processes. These 

 latter are commonly trifid, their segments subulate and alternately cut. The 

 interior (or medullary) cellules are of large size, with valid walls, and are 

 very conspicuous through the semitransparent thin coating of superficial 

 cellules, appearing, under a pocket-lens, like hexagonal areolations. The 

 ceramidia have not been observed. The stichidia spring from the lateral 

 veinlets of the segments or from the midrib, and are excessively branched, 

 dichotomously ; they bear tetraspores singly or in pairs in the swollen upper 

 divisions. The substance is rigidly membranous, and the frond does not 

 adhere to paper in drying. The colour is a dull reddish-brown. 



This fine species is nearly allied to Diet. Iridens, but is a 

 larger and stronger-growing plant, with much less deeply cut, 

 broader, and more obtuse lacinise, stronger midribs, which are 

 well marked even to the extremities, and more conspicuous areo- 

 lations. The areolations in this genus, however conspicuous, 

 are never superficial, the external coating being always formed 

 of minute cellules. Hence the tessellated appearance is more 

 evident under a common pocket-lens than when a higher magni- 

 fying power is employed. 



I bestow the specific name in honour of my friend Dr. Sonder, 

 of Hamburg, who has well illustrated the Algse of Australia in 

 several able memoirs. I had originally referred this plant to 

 l).fimbriata, but erroneously. The latter, to judge by Turner's 

 figure, is much nearer to D. spiralis, if it be distinct. 



Fig. 1. Dictymenia Sonderi, — the natural size. 2. Apex of a segment, — mo- 

 derately magnified, showing midrib, veinlets, false areolations, and shrubby 

 stichidia. 3. Small portion of the same, — more highly magnified, showing 

 the surface-cellules, and the medullary cells appearing through. 4. A 

 branch from a decompound stichidium. 5. A tetraspore from the same: — 

 magnified. 



