GEOLOGY AND PALEONTOLOGY OF THE CANAL ZONE. 5 



the second divisions seem to be omitted and the sporangium is appar- 

 ently mature with onty two spores. Very irregular types of division 

 also occur, and rarely one finds an approach to the zonate x arrange- 

 ment characteristic of most of the Corallinaceae. 



The perithallic cells of A. episporum- appear to be, in the decal- 

 cified state, more rounded and in more moniliform filaments than is 

 the case in A. erythraeum, as may be seen by comparing our photo- 

 micrograph 2 with the photomicograph of a presumably decalcified 

 section of A. erythraeum — published by Lemoine. ;: The distinct strat- 

 ification of the perithallium of A. episporum is due, in part, to the 

 alternation of layers of long and short cells, but we have never seen 

 in the Panamanian species any such striking alternation of long and 

 short cells as is shown in this photograph published by Mme. Le- 

 moine and as is shown still more emphatically in Heydrich's figure 3 * 

 of a vertical section of his Sporolithon ptyehoides. 



From Archaeolithothamnium dimotum Foslie and Howe, 5 the only 

 living species of this genus previously described from the West 

 Indian region, A. episporum' differs widely in its thicker crusts, in 

 its more superficial sporangial sori, which are for the most part ex- 

 foliated after maturity of the sporangia and are only obscurely and 

 imperfectly overgrown, in the usually larger, more rounded, and 

 more moniliately arranged cells of the perithallium, the larger and 

 rather less widely separated sporangial ostioles, etc. 



Archaeolithothamnium curasavicum (K. Martin) Foslie, 6 a Creta- 

 ceous fossil from the island of Curacao, is described and figured as 

 showing distinctly rows of embedded sporangial cavities, such as 

 would not be seen even in a thin decalcified section of A. episporum. 



A Pleistocene fossil, collected by MacDonald at station 6039, from 

 flats near Mount Hope, came from a few kilometers from the locali- 

 ties where we found the plant living, and we can entertain no serious 

 doubt as to the specific identity of the recent and the fossil forms. 

 The living and fossil are similar in external habit, as may be seen 

 bj comparing plates 1 and 4. They are similar also in their rela- 

 tions to old corals, and in structure (compare fig. 1, pi. 2, and fig. 4, 

 pi. 5) they appear to exhibit on\j such differences as may be ascribed 

 to individual variation or as may be expected in comparing the recent 

 or living with the long dead. But little remains of the fossil speci- 



1 Zonately 4-parted sporangia have been described by Foslie for the Californian 

 ArcJiaeolitliothamnium zonatosporum (Foslie, Algologiske Notiser. II. Kgl. Norske 

 Vidensk. Selsk. Skr., 1906, pt. 2, p. 14), so that it would appear that this genus exhibits 

 a wide variety in the matter of division of its sporangia. 



2 Plate 3, fig. 2. 



3 Ann. Inst. Oceanog.. vol. 2. pt. 2, pi. 1. fig. 1. 1911. 

 * Ber. Deuts. Bot. Ges., vol. 15. 1S97. 



5 Bull. N. Y. Bot. Gard., vol. 4, p. 128, pi. 80, fig. 1 ; pt. 87, 1906. 



6 Litliotliamnium. curasavicum K. Martin, Bericht fiber eine Reise nach Niederlandisch 

 West-Indien und darauf gegriindete Studien. II. Geologie, p. 26, pi. 2, figs. 22-25, 1S88. 



