2 PROCEEDINGS OF THE NATIONAL MUSEUM. VOL. 62. 
cells of the large-celled zones, the smaller cells of the small-celled 
zones, and the consequently more pronounced zonation, and in the 
somewhat smaller tetrasporic conceptacles. The conceptacles some- 
times show small pores in the roof with sufficient clearness to leave 
no doubt that the type specimen is a tetrasporic plant of the genus 
Lithothamnium. 
LITHCPHYLLUM TRINITENSE, new species. 
Plates 3 and 4. 
Thallus crustaceous, 0.75-2 mm. thick, becoming superposed, mas- 
sive, and 0.5-3.5 em. thick, the surface nearly smooth, undulate- 
rugose, or broadly and irregularly submammillate, delaminating ; 
vertical fractures showing undulate-plicate zonations 1 mm. or less 
broad; hypothallia usually inconspicuous. the cells 15-262. 10-18p, 
not distinctly “coaxial” or layered; perithallium rather distinctly 
or somewhat obscurely zonate, its cells 9-18 (24)y high and 8-18p 
broad, usually higher than broad, or subquadrate, in very distinct 
layers; conceptacles 320-450p in diameter, becoming embedded. 
A single specimen, more or less embedded, associated with corals 
(?) and occasionally intercalated with Lithoporella melobesioides 
(Foslie) Foslie, and forming the greater part of a mass that is 9 cm. 
long, 5 cm. broad, and 4 cm. thick, in Gasparillo quarry, Trinidad, 
British West Indies, F. W. Penny, No. G 5, station No. 8297 (lower 
Miocene). 
Type in U. S. National Museum, Cat. No. 36605.. 
Of the hitherto described American fossil Lithothamnieae, Lztho- 
phyllum trinitense is perhaps best comparable with L. homogeneum, 
M. A. Howe? from the upper Eocene or lower Oligocene of St. 
Bartholomew, British West Indies, but the thallus appears to strictly 
crustaceous, showing at most only low elevations in place of the well- 
developed branch system of Z. homogenewm and in a thin ground 
section the general structure is seen to be more zonate and less 
homogeneous and the cells of the hypothallium less distinctly “ coax- 
ial” or layered. Conceptacles were not found in L. homogenewm. 
EXPLANATION OF PLATES. 
PLATE 1. 
Lithothamnium pennyi M. A. Howe. 
Fics. 1 and 2. Photographs showing opposite sides, in lengthwise view, of 
the single type specimen, from Matchepoorie quarry, Trinidad, F. W. Penny, 
No. 5, station 8801, natural size. 
3. Photograph of a transverse or slightly oblique section through one of the 
knobs of the above specimen, enlarged 42 diameters. 
2 Carnegie Inst. Washington Publ. no. 291, 1919, p. 14, pl. 1, fig. 1 and pl. 3. 
