CALCAREOUS ALGJE FROM MURRAY ISLAND, AUSTRALIA, 

 AND COCOS-KEELING ISLANDS. 



By Marshall A. Howe. 



Class CHLOROPHYCE^. 



Family CODIACE^. 



Halimeda opuntia (X.) Lamour. 



Halimtda opuntia (L.) Lamour., Hist. Polyp., p. 308, 1816. 



Corallina opuntiaL., p. p. Syst. Nat., vol. 1, p. 805, 1758; Ell. and Soland., Nat. Hist. Zooph., p. no, 1786. 



"800 feet from shore, line I, southeast reef." 



Class RHODOPHYCE.(E. 



Family CORALLINACE.S. 

 Goniolithon orthoblastum (Heydrich) M. A. Howe. 

 Plate 97, figure 2; plate 98, figures i, 2. 

 Lithothamnion orthoblastum Heyd., Ber. deutsch. bot. Ges., Bd. 19, p. 403, 1901. 



Thallus forming closely adherent crusts 0.5 to 3 mm. (mostly 0.75 to 1.5 mm.) thick 

 or becoming 5 to 8 mm. thick through superposition, somewhat plane, or more commonly 

 irregular through following the inequalities of the substratum, or finally showing here and 

 there proper excrescences, these subhemispheric, obtusely subconic, stalactiform, or difform, 

 2 to 10 mm. broad and 3 to 20 mm. high, the surface dull, rather smooth, or in fertile parts 

 becoming minutely foveolate-verruculose; primary hypothallium large-celled and usually 

 conspicuous, mostly 200 to 6oo/i thick, succeeded by alternating, usually sharply defined 

 zones of perithallia and secondary hypothallia, the perithallic zones often abortive 

 and indicated only by a layer of intracellular papillae resulting from the fusion of small 

 potentially perithallic cells to form a layer of the much larger cells of a secondary hypothal- 

 lium; cells of primary hypothallium 30 to 85 /i by 20 to 44 /l(, in distinct or often rather 

 indistinct "coaxial" layers, cells of secondary hypothallia commonly a little smaller and 

 less regularly arranged; perithallic cells mostly 8 to 20/i in longest diameter, abruptly 

 smaller than hypothallic cells, subglobose, ovoid, or difform, often irregularly curved, lobed, 

 or constricted, varying from twice as high as broad to twice as broad as high; "heterocysts" 

 or adventive hypothallic cells of frequent occurrence in perithallic layers, scattered or 

 irregularly grouped; conceptacles small, slightly elevated, subhemispheric, 220 to 320/1 

 in diameter, not becoming imbedded, the usually depressed pore about 25 /u broad. 



From the "Lithothamnium ridge, southeast reef, 1,720 to 1,785 feet from shore." 



In the determination of this remarkable plant, the writer has been able 

 to compare with it original specimens of Lithothamniuvi orthoblastum from 

 the Heydrich herbarium, coming from the Tami Islands, German New 

 Guinea, which is in the same floral region. The correspondence in habit 

 and more especially in structure is so close as to leave no possible doubt as to 

 the specific identity of the two plants. The crusts of Dr. Mayer's specimens 

 are less superposed and consequently somewhat thinner and the proper eleva- 

 tions or excrescences are less numerous and less well developed, being only 

 2 to 10 mm. high and 2 to 5 mm. thick. 



The description as given above is drawn to cover both the original 

 material and Dr. Mayer's specimens, which seem to represent the second 

 recorded collection of this interesting species. Many of the elevations of 



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