The genus Odonthalia, founded by Lyngbye on our O. dentata, 
and nowcontaining three other species natives of the Kamtschatkan 
sea, has been singularly misunderstood by Endlicher, who unites 
with these northern plants of leathery substance and closely cel- 
lular structure, several delicate tropical Alge with highly reticu- 
lated fronds, which have scarcely a character common with Odon- 
thala except that minor one which gives the genus its name,— 
a toothed margin. 
Odonthalia dentata is peculiarly a northern plant. It abounds 
throughout the whole of the European, Northern, Atlantic, and 
North Seas ; and probably extends along the coast of Siberia and 
of North America. In the British Islands, it reaches, perhaps, 
its southern limit, and is most abundant on the coast of Scotland. 
In England it does not appear to be found south of Durham, 
and in Ireland, of Downshire. 
It varies very little in the frond, except that some specimens 
are more luxuriant than others. ‘The mode of branching, and 
alternate pinnati-section is invariable; but the fructification pre- 
sents some varieties. In some specimens, such as I have repre- 
sented, the stichidia are densely clustered, and, as well as the 
bunches of capsules, confined to the axils of the segments; in 
others, both kinds of fruit are scattered along the margm. The 
specimens from which our figure is drawn were kindly communi- 
cated in a fresh state by Dr. Dickie, of Aberdeen. 
Fig. 1. ODONTHALIA DENTATA :—uvatural size. 2. Lacinie bearing capsules. 3. 
Cluster of capsules. 4. Vertical section of a capsule. 5. Lacinie with 
pods. 6. Cluster of pods. 7. A pod or stichidium. 8. Tetraspores. 9. 
transverse section of the lower part of a branch :—all more or less magnified. 
