The genus Odonthalia, founded by Lyngbye on our 0. dentata,
and now containing tliree other species natives of the Kamtschatkan
sea, has been singularly misunderstood by Endlicher, who unites
with these northern plants of leathery substance and closely cellular
structure, several delicate tropical Algæ with highly reticulated
fronds, which have scarcely a character common with Odonthalia
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 ; hut the fructification presents
some varieties. In some specimens, such as I have represented,
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 margin. The
specimens from which our figure is drawn were kindly communicated
in a fresh state by Dr. Dickie, of Aberdeen.
Fig. 1. O d o n t h a l ia d e n t a t a :— natural size. 2. Laciniæ bearing capsules. 3.
Cluster of capsules. 4. Vertical section of a capsule. 5. Laciuiæ witli
pods. 6. Cluster of pods. 7. A pod or sticbidium. 8, Tetraspores. 9.
transverse section of tbe lower part of a braucb :— all more or less ;