ail eet. | 
by a broad transparent border; the joints more or less swollen; all pretty 
uniformly twice or thrice as long as broad, those of the stem occasionally 
somewhat longer. In some specimens the place of tetraspores is occupied 
by roundish bodies (fig. 7.), composed of exceedingly minute, dichotomous 
filaments, radiating from a central point: these may either be regarded as 
viviparous tetraspores, or, possibly, as antheridia. 
en eee 
This species was originally detected in the year 1802, by the late 
Mr. Templeton, of Belfast, at the station where, thirty years 
later, I gathered it, without being at the time aware of the pre- 
vious discovery. Of recent years it has been found on so many 
different parts of the coast, that it must be regarded as one of 
our commoner species; but it does not appear to be generally 
diffused, not having yet been noticed in the west of Ireland, 
although frequent on some parts of the eastern shores. The 
finest specimens I have seen are those collected by Messrs. Hore 
and Rohloff, in Plymouth Sound; a locality which seems pecu- 
harly favourable to the growth of Callithamnzion. 
Callithamnion spongiosum has much the external appearance 
of C. Arbuscula; but its microscopic characters are so different, 
that they belong to separate sections of the genus. It is much 
more nearly allied to C. corymbosum, or the exotic C. granulatum ; 
a south of Europe species, which has so much im common with 
it, that I shall not be surprised if future observations lead to 
their being united. My specimens of that plant are, however, 
not sufficiently perfect to enable me at present to decide the 
question. From C. corymbosum, the duller colour, shorter joints, 
more robust and opake stems, and dense, spongy habit, suffici- 
ently distinguish it. It is curious that it appears to occupy the 
place of C. Arbuscula, on shores where the latter is not found, 
these plants never growing together, though both affect similar 
situations on different shores. 
Fig. 1. CALLITHAMNION sPONGIOSUM: a tuft:—of the natural size. 2. A 
secondary or tertiary branch. 3. A branchlet truncated and _ bearing 
favelle. 4. Spores. 5. A ramulus, with tetraspores. 6. A tetraspore, 
in situ :—more highly magnified. 7. Viviparous tetraspores ? 
