MARINE ALG. 13 
either sessile or very shortly pedicellate, ovoid and bluntly rostrate. The pericarp is 
composed of six or more rows of cells in vertical series. 
Its nearest ally is P. interrupta, which it somewhat resembles in external form ; 
but it differs from that species in having simpler and more lonely dichotomous 
branching (being very rarely or never palmate), and the apices of the branches ligulate 
and not reniform or rotundate. The thallus is not moniliform or torulose, but merely 
opposito-sinuate. P. interrupta is more shortly dichotomous, and often has a triangular 
expansion below its dichotomy, and palmate branching. The constrictions, too, are 
often reduced to almost stalk-like thinness, which is not the case in P. antaretica. 
P. interrupta is an Arctic species, and P. antarctica appears to be its Antarctic 
congener. Possibly they are antipodal polar descendants from a common ancestor. 
P. Brodiei J. Ag. differs in its long stipes cuneately expanded into a more or less 
palmate frond, and is apparently the Arctic congener of the Antarctic P. cuneifolia, 
which has shorter stipes, broader less-lobed frond, and broader shorter lobes with 
shallower sinus. 
13. SPONGOCLONIUM ORTHOCLADUM. 
(Plate IV., figs. 23-25.) 
Frons 8 cm. alta dense fruticulosa, axi centrali erecto tereti rhizoidibus haud 
corticato ramulis ascendentibus velato, quoquoversum ramoso, ramis cauli similibus 
ramulis ultimis longis erecto-patentibus simplicibus strictis subulatis, articulis diametro 
sesquilongioribus, articulo basali nune nudo nune procarpium intra ramellorum 
minutorum fasciculum emittente. Tetrasporangia ignota. 
Cape Adare, January 9, 1902. 
This is a densely bushy plant (fig. 23) of moderate size, about 8 cm. high without the 
basal attachment and without tetraspores, but bearing young procarpia with tricho- 
gynes (figs. 25a, 25b), and so thickly infested with diatoms that it is difficult to obtain 
a clear view of its ramification. S. orthocladum is remarkable for its long straight 
subulate ultimate branchlets (fig. 24), and differs in this respect from all the fruticulose 
Callithamnioid species which we have seen. Its nearest ally is found in certain 
states of S. hirtum [ Callithamnion hirtum Hook. f. and Harv. in Flora Antarctica, IT. 
(1847), pl. Ixxviil., figs. 3 and 4], a plant recorded from the Auckland Islands and New 
Zealand. The typical plant, it is true, differs inter alia in having ultimate pinne 
consisting of a flexuose rachis bearing sub-distichous incurved obtuse ramelli. There is, 
however, in the British Museum a specimen from Cook’s Straits, New Zealand, collected 
by David Lyall and named by Harvey, which, though normal in most respects, yet has 
a few branches which break up into long, straight, subulate ramelf like those of 
our plant. 
