ANTITHAMNION 153 
scheiden sind," the “welche” seems intended to refer, іп fact, if 
not in grammatical syntax, to the "Seitenzweige," and not to the 
" Nebenzweigen ” as interpreted by Kützing and by J. Agardh. А: 
least such an interpretation would remove the only discrepancy 
between Suhr's description and the Callao specimens. 
Antithamnion densum is apparently to be placed with the 
smaller members of the ''Cruciatae" section of the genus, yet 
seems to Бе amply distinct from any of the “Species папае” of 
this group as described by J. Agardh and by De-Toni. It exhibits 
certain points of contact with А. cruciatum (Ag.) Naeg. (especially 
var. radicans J. Ag.), but is smaller, simpler in its branching, the 
branches are less crowded and scarcely “ осећаје" at the apex, 
the pinnae are shorter, more acuminate, more rigid, and more 
fragile, the cells are thicker-walled, and the tetrasporangia less 
elongate; in А. densum the true pinnae are unilaterally pinnulate 
and the pinnules are commonly arranged along the inner or upper 
face of the pinna, i. e., on the side facing the main rachis; in А. 
cruciatum, the true pinna is, as a rule, distichously pinnulate in its 
lower part, at least, and the plane side of the pinna faces the main 
rhachis; in А. densum a careful study of the formation of the 
branches in the apical region shows that they are not always strictly 
distichous (Етс. 9), yet the variations from this arrangement are 
few and inconspicuous as the branches mature, while in A. crucia- 
tum the successive pairs of branches are distinctly decussate and 
tetrastichous; in А. densum, the nearest approach to a 4-verticil- 
late arrangement of pinnae is the occasional formation of an abor- 
tive vegetative branch from the rhizoidal cell at the base of the 
pinna, while in A. cruciatum a 4-verticillate arrangement is said 
to be not uncommon; in A. densum, the mature pinnae are 
acuminate or acute except where the apical cell has fallen off, and 
the conic apical cell is only 5-10 и in greatest transverse diam- 
eter, while in А. cruciatum the pinnae are comparatively obtuse 
and the apical cell is 12-17 и in greatest transverse diameter. 
When, as shown in the figures, it happens that only one distal 
pinnule is elongated, the pinna has a somewhat forked appearance 
and when, in addition, as often occurs, the end of the pinna is 
slightly curved inward, the fork is rather suggestive of the chelae 
of certain Crustaceans. 
