preserving a breadth of from 1-2 lines. Ramification irregular, sometimes 

 dense, with the branches very much divided, and their divisions closely 

 crowded ; sometimes more simple, with fewer and more distant branches. 

 In all cases however the lacinise of the frond are either ternate or quater- 

 nate, in which case the uppermost of the three secund lacinise has a tendency 

 to lengthen into a branch, while the lower remain as cultrate, tooth-like 

 processes. The ultimate juiimdes are 1-2 lines long, incurved or somewhat 

 falcate, subacute, and more or less distinctly toothed along their outer edge, 

 or rarely subentire. Faint indications of a midrib are seen in some spe- 

 cimens in the pinnae ; and in old fronds the stem and the principal branches 

 are thickened in the middle and plano-convex. The conceptacles are soli- 

 tary, about as large as poppy-seed, dark-coloured and very opaque, warted, 

 and sessile on the edges of the branches ; they are very irregularly scattered, 

 occurring either above or in the axil of the pinnules or on the opposite edge 

 of the branch : their pericarp is very thick. The sticJiidia are more con- 

 tantly in the axils, and are falcato-fusiform, simple, tufted, containing a 

 single row of tetraspores. The colour is a brilliant crimson, becoming 

 brighter in fresh-water. 



The genus Plocammm, which has but one representative in the 

 northern hemisphere, has many southern species, distributed 

 chiefly in AustraUa and South Africa. Of these the present is 

 a beautiful and readily known and abundant species, differing 

 from most of the Australian kinds in having sessile conceptacles, 

 and ramuli alternating in threes, not in twos. In both these 

 characters it agrees with the cosmopolitan P. coccineum, from 

 which it is readily known by the warted conceptacles and denti- 

 culate edges of the ramuli. 



Fig. 1. Plocamium Preissianum, — tJie natural size. 2. Part of a pinna, with 

 conceptacles. 3. Vertical section through a co/^cp^ifaeZe and branch. 4. Part 

 of a pinna with axillary stichidia. 5. Three of the sticJddia removed. 

 6. A tetraspore : — the latter figures variously magnified. 



