(129) 
cells rather numerous: sporangia cae broad, eae pw long, ex- 
clusive of apiculum, the latter 15-25 long. (PLATE 80, F. 
B87. 
Porto Rico: On rocks at low-water mark, Lemon Bay, near 
Guanica (xo. 2 
Among recent species of this genus, hitherto known, Archaeolitho- 
thamnion dimotum stands nearest A. erythraeum (Rothpl].) Fosl., 
but, is, in fact, more closely connected with the fossil species A. 
curasavicum (K. Mart.) Fosl. The latter seems to have grown in 
the same manner and the crust is of about the same thickness as in 
A. dimotum. Yn other respects, also, the two species are closely 
allied, except that the cells in A. dzmotum seem to be generally a 
little smaller than in A. curasavicum.* According to a section of 
A. curasavicum which Professor K. Martin kindly sent for ex- 
amination, the cells in some parts of the crust are of the same shape 
and size as in A. dimotum, but in other parts they are frequently 
larger, attaining a length of 20, though often less. A. curasave- 
cum is ‘*aus zweifellosen Kreide-Ablagerungen herktinftig,” ac- 
cording to a kind communication from Professor Martin; A. dz- 
motum shows, in our opinion, sufficient diversity in structure to be 
considered distinct, even though only a single and perhaps poorly 
developed specimen of it has been seen; it is the rey recent species 
of the genus known from America. 
Lithothamnion mesomorphum ornatum var. nov. 
hallus much more delicate than in the type, only 150-2004 
thick, proliferations smaller: fypotliallic (medley) cells 11-20 x 
—I1 pz, those near the lower surface often very narrow 
2 x 
3-6 with large intercellular pee perithellie cells Gave 
upper surface) mostly r rounded or subquadrate-oblong in vertical 
section, 4-9 in diameter, (PLATE 80, F. 2; PLATE 90, F. 2. 
Banamas: Cave Cays, Exuma Chain, low littoral ona rock-shelf 
under an overhang (70. go2r). 
The plant is yellowish-pink or salmon-colored when living. All 
the specimens examined are apparently sterile, yet we believe that 
they are to be looked upon as representing a variety of Lzthotham- 
nion mesomorphum Fosl. (New Melob. 5. 1901), originally de- 
scribed from Bermuda. In habit, the plants approach delicate 
forms of ZL. lichenotdes. 
*Martin, K. Bericht iiber eine Reise nach Niederlandisch West-Indien 
und darauf been Studien. II. Geologie. p. 26. Leiden, 1888. 
