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REPORT OF THE COMMISSIONER OF FISH AND FISHERIES. 115
P. DUBYI, Crouan; Phyc. Brit, Pl. 71; Florule du Finistère, Pl. 19, Fig. 130; Proc. Am.
Acad. Arts & Sciences, 1877, p. 239.
Fronds dark purple, thin, completely adherent to the substratum, somewhat
calcareous beneath; cystocarpic spores few in number (4-6), arranged in one or two
rows.
On shells and stones at low-water mark and in deep water.
Eastport, Maine; Magnolia, Mass.; Europe; California.
As yet only found in a sterile condition, apparently not common. The species might possibly be
mistaken for Petrocelis cruenta at first sight. It is, however, more decidedly reddish and thicker. Under
the microscope the structure of the frond is seen to be parenchymatous throughout, while in Petrocelis
the vertical filaments are nearly free from one another. P. imbricata, Kütz., Tab. Phyc., Pl. 90, from
Newfoundland, is a doubtful species, which is not likely to be recognized by future botanists.
PETROCELIS, J. Ag.
(From πετρος [petros], a stone, and κηλις [kelis], a stain.)
Fronds gelatino-coriaceous, horizontally expanded, indefinite in outline, adhering
closely to the substratum, vertical filaments united below, but above rather loosely
held together by a gelatinous substance; antheridia and cystocarps unknown;
tetraspores spherical, cruciate, formed directly from some of the cells of the vertical
filaments.
A genus represented by a single species, which is widely diffused in the North Atlantic. At once
recognized by the peculiar position of the cruciate tetraspores, which are in the continuity of the
vertical filaments. There is usually only a single tetraspore in each filament, but Ruprecht, in
Phycologia Ochotensis, figures a form in which several contiguous cells are transformed into
tetraspores.
P. CRUENTA, J. Ag. (Cruoria pellita, Harv., in Phyc. Brit., Pl. 117, non C. pellita,
Lyngb.) Pl. 14, fig. 1.
Covering rocks and stones near low-water mark with a dark purple, velvety stain.
Common from Nahant northward; Europe.
The present species often accompanies Hildenbrandtia rosea, from which it is distinguished at sight by
its darker color and velvety gloss when moist. It is also decidedly thicker and more easily scraped from
the rocks. The species is not yet known south of Cape Cod, but may be expected. The fronds of the
present species are infested by a green unicellular parasite, which is frequently seen in the shape of
ovoid sacks, drawn out at the lower end into a slender stalk amongst the vertical filaments. It is, in all
probability, the parasite mentioned by Cohn, in Ueber einige Algen von Helgoland, as occurring in
Cruoria pellita, to which, as far as we know, no name has as yet been given.
HILDENBRANDTIA, Nardo.
(Named in honor of Prof. Franz Edler Hildenbrandt, of Vienna.)
Fronds crustaceous, without calcareous deposit, forming thin, reddish, horizontal
expansions of indefinite extent, composed of cuboidal cells arranged in vertical lines
and arising from a horizontal basal layer;