292 PAPERS FROM THE DEPARTMENT OF MARINE BIOLOGY. 



the thallus of L. orthoblastum are obviously due to its close adherence to 

 worm-tubes and other salient irregularities of the substratum, but a cross- 

 section or fracture of these elevations indicates that they are also often proper 

 excrescences. 



Among the remarkable characteristics of L. orthoblastum are the very 

 large cells of the hypothallium, which give the lower part of the thallus in a 

 vertical fracture an alveolate-vesicular appearance under a hand lens. 

 Another striking and apparently constant peculiarity is the presence of numer- 

 ous layers of hypothallic cells with intracellular papillae from their basal faces, 

 these cells and papillae evidently resulting from the fusion of the much smaller 

 cells of an abortive or suppressed perithallic layer. This character was not 

 mentioned by Heydrich in his description of the species and, so far as the 

 present writer knows, nothing quite comparable has hitherto been recorded 

 for any species of the Lithothamnieae, though Mine. Lemoine 1 has mentioned 

 the frequent fusion of two cells to form one in Lithothamnium calcareum. 



The generic position of this plant is open to question, but the present 

 writer believes that it has more in common with the species currently referred 

 to Goniolithon than with those that are now referred to Lithothamnium. 

 Heydrich believed that he saw rudimentary or immature sterile sori of the 

 sort that characterize the genus Lithothamnium as now interpreted. He says 

 in regard to this: 



"Der sterile Sorus besteht somit nur aus der flachen, 250 n im Durchmesser 

 fassenden Decke, welche 5-10 /x iiber die Cuticula hervorragt und von fast 100 Pori 

 durchbrochen wird. Die einzelnen Pori sind deutlich und leicht in der Flachenan- 

 sicht zu unterscheiden, konnen aber in einem entkalkten Langsschnitt kaum nach- 

 gewiesen werden. Eine eigentliche Hohle entsteht mithin nicht, wohl aber wird 

 durch die abfallende Decke eine kleine Vertiefung zuriickgelassen." 



The present writer also has observed, both in the New Guinea and the 

 Murray Island specimens, minute pores arranged somewhat as in a Litho- 

 thamnium sorus and sometimes on a slight elevation, but the pores are smaller 

 than in ordinary species of Lithothamnium and sections show only immersed 

 flask-shaped cells about 40^ high and 20pt broad, looking a little like the 

 sporangia of an Archceolithothamnium, but probably representing some para- 

 site or endophyte or cells that have been occupied by some such foreign 

 organism. Occasionally a second cell is observable at the base of such cells, 

 appearing to penetrate the tissues of the host after the usual fashion of endo- 

 phytes or parasites. The flask-like cells have snout-like prolongations that are 

 carried a little beyond the general surface, and the exserted snout often shows 

 a flaring mouth through which the contents of the cell are apparently dis- 

 charged. These groups of immersed flask-shaped cells certainly occur on the 

 same individuals that bear the ordinary conceptacles referred to in the above 

 diagnosis — sometimes within 0.5 mm. of the ostiole of such a conceptacle. 



■Ann. Inst. Oceanog., t. 2, fasc. 2, p. 64, 191 1. 



