83 



the crust as well as the knobs, but they are more or less indistinct 

 and partly wanting in old specimens. 



The colour is much fugitive. I have not noted that of fresh 

 specimens, but dried ones partly are yellowish-white partly yellowish- 

 brown and occasionally with a purplish tinge. 



The structure is rather varying, as in most other Lithothamnia.. 

 However, the cells of the inner layers of tissue are in a longitu- 

 dinal section of a knob frequently longer in proportion to the 

 thickness than for inst. in L. polymorphum, and the walls appa- 

 rently thinner, about 10 — 17 ji long and 6 — 10 p. thick in the 

 specimens that I have examined. 



The organs of propagation are as a rule very scarce and 

 apparently seldom attain fully development. They are often attacked 

 by animals, and in most of the conceptacles of sporangia that I 

 have examined I did not succeed in finding spores, or I met with 

 small animals or animal substance fully filling the cavity. The 

 named conceptacles are irregularly scattered over the crust or knobs 

 and never so numerous as in L. polymorplium, very nearly related 

 to those of L. glaciale in appearance as well as development, 

 though less distinctly marked, convex but very little prominent, 

 and seen from the surface 300 — 350 \i in diameter, sometimes a 

 little more sometimes less. The roof is intersected with 30 — 40 

 canals, which are crowded in the central portion of the roof. These 

 canals are larger than those in L. glaciale. The central portion 

 often gets somewhat depressed when nearly dissolved, and then 

 it looks, in a certain stage, as if the conceptacles were surrounded 

 by an annular border, as in L. glaciale. Most of the certainty 

 few sporangia that I have seen were bisporic, about 100 — 130 /^ 

 long and 25 — 35 ft broad, but probably attaining larger size, nearly 

 linear, or a little broader in the middle than towards the ends. 

 However, in another specimen certainly somewhat differing from 

 typical f. irregularis in habit, but most probably belonging to this 

 form I found a conceptacle containing irregularly two- three- and 

 four-parted sporangia. It may, therefore, be, that the sporangia 

 have not been fully developed and mature ones in fact are 

 tetrasporic. 



