12 GEOLOGY AND PALEONTOLOGY OF THE WEST INDIES. 



sections made from decalcified material of authentic A. sibogce furnished 

 by Madam Weber, the perithallic cells often seem larger 'than these 

 measurements would indicate, yet the cells are rarely more than 13 /z 

 long, while in our fossil plant most of the cells, in radio-vertical section, 

 are more than 13 /x long. Moreover, our sections of A. affine are mostly 

 oblique and our measurements may not do full justice to the length of 

 its cells. Numerous "minute square and oblique intermediate cells 

 * * * 2 to 4 /i in diameter," ascribed to A. sibogce, we have not 

 observed in A. affine. 



The sporangial cavities are numerous and they appear in thallus 

 sections sometimes in rows of 30 or 40. Some of the embedded sori 

 are near the surface and others are so close to the medulla that two- 

 thirds of the radius of the thallus-branch would lie external to them. 



Archceolithothamnium curasavicum (K. Mart.) Foslie, 1 a Cretaceous 

 fossil from the island of Curasao, is described and figured as having a 

 crustaceous rather than a terete fruticose thallus. Martin's figure 23, 

 however, looks a little like a cross-section through an eccentric terete 

 thallus, but it is described as a longitudinal section and is probably 

 designed to represent the coralline as attached to and partially inclosing 

 some foreign object, an explanation that gains support from the 

 author's description of the plant. 



Of the hitherto described fossil species of Archceolithothamnium, A. 

 affine is probably best compared with A. turonicum (Rothpl.) Fosl., 2 

 from the Turonian of Le Beausset, Dep. Var, France, but it is coarser, 

 having branches 3.5 to 6 mm. instead of 3 mm. in diameter. 



Genus LITHOTHAMNIUM Philippi. 



Lithothamnium concretum, new species. 



(Plate 1, Figure 2; Plate 2.) 



The following is a description of this species : 



Thallus forming irregularly hemispheric, subglobose, or ellipsoidal, solid or 

 more or less hollow, concretionary masses, mostly 2 to 5 cm. in diameter, the 

 surface exhibiting a few rounded, slightly pronounced irregular knobs or 

 lobes, these usually 5 to 15 mm. broad and 5 to 8 mm. high; medulla irregularly 

 oblong in section, 5 to 15 mm. broad, becoming hollow on exposure; weathered 

 fractures of thallus showing numerous tortuous or irregularly plicate more or 

 less concentric lamellae, these mostly 0.5 to 1.0 mm. thick, at length somewhat 

 elevated or solute; cells of primary medullary hypothallia 8 to 13 n broad; 3 

 secondary hypothallia infrequent, 100 to 170 ju thick, scarcely "coaxial," their 

 cells 14 to 18 fj. (rarely 26 ju) by 8 to 13 /x; perithallium conspicuously, sharply, 

 narrowly, and irregularly zonate, its larger cells 10 to 15 /i by 8 to 12 /i, its 

 smaller 8 ju by 6 M or subquadrate (8 to 11 /x square) or occasionally broader 



1 Lithothamnium curasavicum K. Mart. Bericht iiber eine Reise nach Niederlandisch Weat- 



Indien und darauf gegriindete Studien. II. Geologie, 1888, p. 26, pi. n, figs. 22 to 25. 



2 Lithothamnium turonicum Rothpl. Zeitschr. deutsch. Geol. Ges., vol. 43, 1891, pi. xvi, figs. 9, 13. 



[Plate is wrongly numbered xv.] 



3 Not well shown in longitudinal view in the sections thus far made. 



