17 



Siboga expedition shows, however, that the two forms mentioned represent different species, 

 and that the tvpical specimen from the Gulf of Siam has been young. The plant assumes 

 thicker and more extensive crusts, vvhich however are rather varying, and the conceptacles ot 

 sporangia generally prove to be larger than in the specimen mentioned. I therefore place it 

 here as an independent species. 



In a young stage the plant clings closely and rather firmly to the substratum. Even 

 when advancecl, it may be fairly closely adherent, though it is in part gradually detaching 

 itself. On a large and even substratum the crust becomes rather smooth (PI. I, hg. 24). If the 

 substratum is small and branched, it certainly conforms fairly to it in shape, but is more 

 loosely attached to it or partly growing quite freely. PI. I, fig. 25 shows a form growing 

 on corals, partly loosely encompassing the branches of the coral, partly even distended between 

 the latter. This form comes also nearest to the typical one. If the plant is charged with 

 extraneous objects, new crusts are formed above, which give rise to irregular or branchlike 

 formations. Cp. PI. I, fig. 21, representing a form intermediate between f. typica and f. crispescens, 

 however most closely allied to the latter This form is distinguished by its thallus being more 

 or less lamellate and crispate, or plicate-leaf-like (PI. I, fig. 22 — 23). It corresponds partly to 

 Lithoihamnion l J /ii/if>pü f. crispata, partly to L. Engelhar tii f. imbricata and f. pseudocrispata*), 

 with which forms it has partially much in co'mmon, though distinctly separated particularly as 

 to the conceptacles of sporangia. The form seems peculiarly to rise, when the substratum is 

 irreeular or of less firm consistency. 



The species is attached to different objects, partly to shells of molluscs, partly and 

 particularly to corals, calcareous sediment or other calcareous algae. Thus the specimen pictured 

 in pi. I, fig. 24 has coalesced with Archaeolilhotkamnion crxtliracum. which it partly covers. 

 A small portion of the last mentioned alga is to be seen at the bottom of the picture. The 

 same specimen is also quite covering a young Goniolithon Reinboldi. It sometimes anastomoses 

 with Lithoihamnion fragilissimum, and it even occurs on rather fine- 

 branched species, as Lithophyllum moluccense and L. Bamleri, but 

 is here less typical. So also when it sticks to Archaeolithothamnion 

 timorense. The plant is thus less dependent on the substratum than 

 several other species. ^ ^^^mp .ju^^. 



Sections of the crust show that the hypothallium is frequently ^i l±;iiHH^(f;ééf(i£^$0iiiL 

 marked coaxial. The cells of this layer are 12 — iS ij., or now and ' v 



then up to 22 p.. long by a breadth of 6 — 1 2 <j.. The perithallium is Fig . 7 . LitkothamnhnsimuiansSoA. 

 slightlv developed, especially in such parts of the crust which are A - Vertical section of a crust vather 



ö J c i. j 1 adherent to the substratum; X 72- B. 



growing more or less freely. Sometimes it may, however, be rather Radial section of a part of a crust 

 vigorous and even stratified. The cells are square, often with rounded e 



corners, 5 — 7 u. in diameter, or slightly vertically elongated, in the latter case here and there 

 up to 1 2 ij., long; tig. 7. 



1) This form from Tasmania, referred by Hevdrich to Lithothamn, -iim Hauck, I have classified in Melob. Arb. Heydr. 



p. 27 as a denominated form of L. Engelliartii. It is, however. possible that it only represents a more irregular L. Engelhartii f. imbricata. 

 I have only seen a sterile specimen. 



SIBOGA-EXPEDIT1E LXt. 3 



