THE MAKIXi: ALO.i: OK NKW KNdLAND. 115 



P. DUBYI, Crouan; Tliyc. Brit., Tl. 71; Florule dii Fiuistorc, PI. 10, 

 I'i-:. 130: Proc. Am. Acad. Arts c^' Sciences, 1877, p. 239. 



Fi*onds dark puri)le, thin, completely adherent to the snbstratum, 

 somewhat calcareous beneath; cystocarpic spores lew in number (4-C), 

 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 Kpecies 

 might iH>ssil)ly be mistaken for Petrocelis cruenta at tirst sight. It is, however, more 

 decidedly roddish and thicker. Under the microscope the structure of the frond is 

 seen to be parcmhymatous throughout, while in PetrocdiA the vertical filaments are 

 nearly free from one another. P. imhricata, Kiitz., Tab. Phyc, PI. IK), from Xewfound- 

 lautl, is a doubtful speiitvs, which is not likely to-be recognized by futuri' botanists. 



PETROCELIS, J. Ag. 



(From :Terf>o-, a stone, and Kif/.i-, a stain.) 

 Fronds gelatino-coriaceous, horizontally expanded, indelinite in out- 

 line, 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 iu the North At- 

 lantic. 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 tetra- 

 spore in each filament, but Ruprecht, in Phycologia Ochotensis, figures a form in which 

 '^•^^•eral contiguous cells are transformed into tetraspores. 



P. CRUENTA, J. Ag. {Cruoria peUita^ Ilarv., in Phyc. Brit., PI. 117, 

 non C.jyeUita, Lyngb.) PI. 14, fig. 1. 



Covering rocks and stones near low-water mark with a dark purple, 

 M'lvety stain. 



Common from Xahant northward; Europe. 



The pre«ent species often accompanies Ilildenbrandtia rosea, from which it is dis- 

 tinguished at sight by its darker color and velvety gloss when moist. It is also de- 

 cidedly thicker and more easily scraped from the rocks. The species is not yet known 

 south of Cape Co<l, but may be expected. The fronds of the present species are 

 infested by a green unicellular parasite, which is fre(iuently 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 Teber einige Alg«Mi von 

 Helgoland, as occurring in Cruoria ptUita, to which, as far as we know, no nauu' has 

 as yet been given. 



IIILDEXBRAXDTIA, Nardo. 



(Named in honor of Prof. Franz Edler JJildenbrandl, of Vienna.) 



Fronds cni.staceous, without calcareous deposit, forming thin, reddish, 

 horizontal expansions of indefinite extent, composed of <uboidal cells 

 arr:m-_'«*(1 in v.-rtjcul lines and arising from a horizontal bns:il l:iver; 



