Postelsta 260 
The nearest relatives of the present genus 
are obviously Laminaria and Cymathere. Phyl- 
laria also is similar in appearance but has 
numerous cryptostomata on the lamina which 
are wanting in Renjrewia even when young. 
Cymathere differs in the folded lamina. The 
various species of Laminaria have forking sec- 
ondary hapteres. Evidently the lack of hap- 
teres, mucilage ducts and strengthening tissue, 
together with the simplicity of its body, mark 
this as one of the most primitive of kelps repre- 
senting a form close to the original ancestor from 
which all kelps, with the possible exception of 
the aberrant Chorda and Adenocystis, have been 
derived. 
The two species with simple _holdfasts, 
previously described as Laminarias are both 
distinct from the present species. 
Laminaria solidungula J. G. Agradh. (De 
Kammanaceis Sym. Of. ps8. 1807.) swhich 1s 
very completely described by its author, pre- 
sents several points of divergence. It is con- 
siderably larger than Renfrewia parvula and 
has well developed mucilage ducts. Its habit 
