34 DASYCLADEyE. 



which completely encases the frond and conceals its filamentous structure. In Cymopo- 

 lia, again, we have a still further advance in structure ; for, not to speak of its calcareous 

 shells, every node of which the branching frond is composed may be compared to the 

 whole frond of a Dasydadus or a JSfeomeris. Like them, it is a tubular axis whorled 

 with ramelli ; but these latter are so closely placed together that the whorled character 

 is not obvious, and the branch has the mamraillated look of a Codium, if its calca- 

 reous shell be removed ; or of a piece of honeycomb, if viewed with the shell still 

 remaining. 



The spores are of large size, and are always formed within proper fruit-cells or spo- 

 rangia, and, so far as I am aware, are destitute of vibratile cilia, and appear to be 

 formed on a much more perfect type than ordinary zoospores. They have a tough, 

 hyaline, membranous coat, and enclose a mass of dense, dark green or brown endo- 

 chrome. In Polyphysa and Acetabular ia the sporangia spring directly from the axial 

 tube ; in Dasydadus, Neomeris, and Cyrnopolia they are found on the ramelli, and 

 are either special cells, developed in the axils of the ordinary cells (as in Dasydadus), 

 or are formed by metamorphose of a division of the ramellus, as in Cyrnopolia. 



All the plants of this order, with the exception of Dasydadus, secrete carbonate of 

 lime, but in very different proportions. In Polyphysa and Acetabularia the calcareous 

 matter exists as a thin varnish to the surfoce of the stem ; but in Cyrnopolia it forms 

 as complete a shelly envelope as it does in one of the calcareous polypes, and indeed a 

 dead frond in this genus might readily be mistaken for the husk of a zoophyte : its 

 honeycombed pores closely resembling polype-cells. 



All the species are natives of the warmer parts of the sea. Dasydadus and Aceta- 

 bularia have representative species in the Mediterranean ; and the latter is found also 

 in the tropical Pacific. Neomeris, which may probably yet be detected on the Floridan 

 Keys, has species in the West Indies and Pacific Ocean. Cyrnopolia is found in the 

 Carribean Sea, and also at the Canary Islands. Polyphysa was discovered by Dr. R. 

 Brown at King George's Sound, and has recently been found at Port Lincoln, Australia, 

 by Mr. Wilhelmi ; and at Swan River, by Mr. George Clifton. 



I am very unwilling to multiply families, especially among plants of such low 

 organization as the Chlorospermatous Algae, and yet I have been in a manner com- 

 pelled to remove from the Siphonaceoe both the little group now described, and the 

 following one (Valoniacece); from the impossibility of devising any diagnostic charac- 

 ter which would include the whole. The true Siphonacece are typically known by being 

 wholly formed of long, tubular branching ceUs. In the Dasydadece the axis only is 

 of this character ; the rest of the frond consists, as in Conferva, of strings of short 

 cylindrical cells ; and the spores are of a higher type than in Sip)honacece. In Valo- 

 niacew tubular branching cells are found, if at all, only in the root, or in a spongy caudex, 

 while the principal part of the frond is formed of confervoid filaments. They approach 

 Dasydadece through Chamcedoris, and possibly Kiitziug may be correct in associating 

 them, as he has done in his latest arrangement, with this group ; but, ignorant as we 

 are of their proper fructification, I have not ventured to adopt this course. The habit 

 of the true Valoniacece is dissimilar, and in none of them do we find the ramclliferous 

 internodes which characterise the present family. 



