86 NEMALIONACEAE 
14. A young unbranched plant with a terminal monosporangium. 
15, 16. Plants with short secund branches and hamate-arcuate axes. The mono- 
sporangia are here secund and sessile or terminate the short branches. 
17. A plant with alternate, opposite, and irregular branching. 
18. A plant with secund branches, of which the lower are longer than the main axis 
here shown in a horizontal position). 
All figures from plants on Chaetomorpha (La Punta, region of Callao, Coker 38 
р.р.). Figures 12 and 13 аге enlarged 675 diameters; 14-18, 390 diameters. 
Acrochaetium clandestinum (Mont.) comb. nov. 
Callithamnion clandestinum Mont. Ann. Sci. Nat. Bot. II. 8: 350. 
1837; Fl. Boliv. 15. pl. 7. f. 2. 1839. 
Epiphytic, with a well-developed multicellular unistratose 
basal disc of more or less coherent creeping filaments; erect fila- 
ments rather loosely cespitose, penicillate, or pulvinate, 0.5-1.2 
mm. high, broadest near the middle, tapering towards the base 
and very slightly towards apex, 5.5-8.0 и in diameter near base, 
8-11 u in middle and about 8 и at apex, sparingly branched in the 
lower half, rather freely branched and often fasciculately decom- 
pound in the upper half, the branches secund, irregularly alternate, 
- 
or occasionally opposite, the ultimate ramuli 5-8 u in diameter; P 
cells mostly 3-6 times as long as broad, becoming 2-3 times in the 
ramuli and at the apices; chromatophore single, parietal, often 
deeply lobed, or sometimes apparently divided into two or more 
separate parts, occasionally somewhat ribbon-shaped, pyrenoid 
lateral or very commonly at one end of the cell; hairs apparently 
wanting; monosporangia 8-11 и long, 4.5-5.5 и wide, thin-walled, 
rather diaphanous and inconspicuous, mostly in pairs or solitary 
at the apices of one- or two-celled, usually secund, often irregularly 
alternate, or rarely opposite ramuli, occasionally sessile or terminal 
on the main branches, the basal cell of the two-celled fertile ramuli 
commonly bearing a latero-terminal sporangium, the sporangia 
all smaller than the supporting cells. [PLATE 31, FIGURES 19-24.] 
On Chaetomorpha and Cladophora fascicularis in beach drift, 
La Punta, region of Callao, January 25, 1907, Coker 38 p-b- 
associated with various other epiphytes, as indicated under 
Acrochaetium catenulatum. 
The original specimens of Montagne's Callithamnion clandes- 
tinum (on Cladophora fascicularis, Callao, d'Orbigny) we have been 
enabled to see through the obliging kindness of the curators of 
the herbarium of the Muséum d'Histoire Naturelle of Paris. 
The material, which is fastened to two small pieces of mica, is 
meager and we have not felt justified in attempting to remove any ` 
