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form, rendering it very easily confounded with otlier species. It gene- 

 rally foi'ms close velvety j)n,tches on the stems of Laminaria digitata, 

 to which it is said to be most partial, and may be generally recognised 

 by its creeping rhizome from the other species with which it is likely to 

 be confounded, and from C. Turneri by the great disparity in the length of 

 the joints. When wholly unbranched it very closely resembles C. sparsum, 

 and may be distinguished by its rather stouter more rigid stems, and the 

 larger articulations. We have seen no fruit of either kind, and presume 

 it to be imcommon. 



CALLITHAJINION PLUMA. 



EXPLANATION OF DISSECTIONS. 



Fig. 1. — Portion of a plant. 

 2. — Terminal tetraspore. 

 3. — Lateral tetraspore. All maguifiecL 



