42 



sometimes even nearly towards the peripherical portion, and then 

 the branches often become still denser and more anastomosed than 

 if not or only a little attacked. PI. 10, fig. 3. Therefore, it fre- 

 quently becomes rather hollowed, or the cavity filled with boring- 

 muscles, seldom intersected, but occasionally opened either in the 

 part turned upwards or in the lower part and rubbed, or even 

 getting a nearly cup-shaped form, and the interwalls between the 

 branch-systems visible from this side. However, this appears only 

 to be caused by the animals, in part together with the compres- 

 sing and denudating influence of rapid tides, as the plant apparently 

 not exhibits any tendency to open and to develop itself in this 

 direction, like some other Lithothamnia. In such specimens the 

 branches of the peripherical portion around the opening often get 

 rather denudated, so that only the half of a branch or less may 

 be left in a longitudinal direction of the axis, which also appears 

 to be caused by the influence of the water, and so also partly in 

 regard to the much varying shape of the tip of the branches. The 

 surface of the frond is in general smooth, sometimes, how r ever, the 

 apex of the branches, or other and especially denudated parts of 

 the plant are furnished with scaly thickenings, or new local for- 

 mations of tissue. 



The structure of the frond frequently appears to be a little 

 coarser than for inst. in L. fomicatum. The cup-shaped layers 

 of tissue are, in a longitudinal section of a branch, shown to be 

 distinct and rather regular, if not too much disturbed by the hur- 

 ried conceptacles of sporangia. The inner cells of the named layers 

 are about 12 — 16 /x long and 6 — 8 fx thick. 



I have seen but some few specimens bearing conceptacles of 

 sporangia, and I have not met with cystocarpic ones. The first 

 named organs occupy a frequently sharply defined zone below the 

 tip of the branches, and apparently most often in great numbers, 

 as in L. tophiforme, and the roofs' sometimes even confluent, often 

 much resembling the conceptacles in the latter, however, in general 

 a little smaller, or 400 — 450 jx in diameter, seldom less. In a 

 younger stage of development they are convex, very little promi- 

 nent and not distinctly marked, and, therefore, easily confounded 



