14 GEOLOGY AND PALEONTOLOGY OF THE WEST INDIES. 



perithallium in more manifest vertical rows; in radio- vertical sections 

 of L. concretum it is the horizontal or concentric alignment of the peri- 

 thallic cells that is the regular and obvious thing (see plate 2), while in 

 L. lacroixi the vertical or radial alignment would often appear to be 

 more manifest. 



Genus LITHOPHYLLUM Philippi. 



Lithophyllum homogeneum, new species. 



(Plate 1, Figure 1; Plate 3.) 



The following is a description of this species: 



Thallus massive or coarsely subfrutescent, forming concrescent masses 7 to 

 18 cm. (or more?) broad, the main branches or axes subterete, subtrigonous or 

 irregularly flattened, 5 to 20 mm. in diameter; weathered fractures showing 

 rather indistinct irregularly concentric lamellae, these 'ess than 1 mm. thick; 

 cells of both hypothallium and perithallium in regular layers; secondary 

 hypothallia of rare occurrence; cells of hypothallium 20 to 26 \x by 8 to 13 n; 

 perithallium for the most part obscurely, or now and then distinctly, zonate, 

 rather homogeneous in structure, its cells mostly 13 to 20 \i by 10 to 13 n, 

 occasionally reaching length of 25 fi; concept acles unknown. 



Embedded in limestone (upper Eocene or lower Oligocene), above 

 head of Governor's Bay, St. Bartholomew, T. W. Vaughan, station 

 No. 6923, February 22, 1914. 



In its massive, coarsely subfrutescent habit, Lithophyllum homo- 

 geneum may have borne some resemblance to the recent L. antillarum 

 Foslie and Howe, 1 but it is very different in structure, having a gen- 

 eral ground substance of much larger cells and failing to show (in sec- 

 tion) the short rows of enlarged cells which characterize Foslie' s genus 

 or subgenus Porolithon. 



Among the fossil forms, a weathered section of one of the coarser 

 branches of Lithophyllum homogeneum may bear a slight superficial 

 resemblance to Lithothamnium concretum M. A. Howe (Antigua, 

 Vaughan, No. 6862), but a prepared section shows a much more homo- 

 geneous, less zonate structure, with larger cells. Conceptacles have not 

 been identified with certainty, but the vegetative structure suggests 

 that its place is with Lithophyllum rather than with Lithothamnium. 

 A possible relative is the plant from Oligocene strata at "Astrup bei 

 Osnabruck," Germany, described and figured by Gumbel 2 as Litho- 

 thamnium tuberosum and afterwards described by Rothpletz. 3 The 

 specimens of the latter were apparently free, while Lithophyllum 

 homogeneum is embedded, so that it is somewhat difficult to compare 

 the two as to external form, but L. homogeneum is probably a more 

 frutescent and less crust aceous plant, with branches, or some of them, 



1 Bull. Torrey Bot. Club, vol. 33, 1906, p. 579, fig. 2 and plates 25, 26. 



8 Abhandl. mat.-phys. CI. k. bayer. Akad. Wiss., vol. 11, abth. 1, 1871, p. 39, plate I, figs. 5a, 56, 5c. 



* Zeitschr. deutsch. Geol. Ges., vol. 43, 1891, p. 317, 318. 



