136 Rhodora [May 
range of the species in an interesting way, shows what possibilities 
still remain for any intelligent botanist, even with little previous 
knowledge of algae. Very likely there are many collections similar 
to Miss Cherrington’s which when examined might yield results of 
equal interest. 
During the past summer two species have been found on our coast, 
which appear to be new, and which are characterized as follows. 
Isactis centrifuga Bornet ms. Frond dark green or nearly 
black, up to 4 cm. diameter, growth marginal, the central portion of 
the frond becoming detached from the substratum and rounding 
upwards, while the margin remains closely attached. Filaments 
8-12 y diam., slightly swollen at base, reaching a length of a milli- 
meter; sheath firm, usually translucent, sometimes brownish and 
opaque ; trichomes 8—ro y diam., cells one third to one half as long 
as wide; heterocysts basal, spherical or depressed ; rarely intercalary, 
spherical or elongate. On rocks near low water mark, Ochre Point, 
Newport, R. I., May 26, 1900. — Dr. E. Bornet in litt. 
This plant was at first supposed by the writer to be Rivularia 
Polyotis (J. Ag.) Born. & Flah. which might be expected on our 
coast; but on submission of specimens to Dr. Bornet, the latter 
pointed out the distinctly marginal growth of the frond, which would 
refer it to the genus Isactis. ‘This genus has hitherto been mono- 
typic, Z. ^/ana (Harv.) Thuret, growing on algae, shells and stones, 
being found in the Mediterranean and in the warmer waters of both 
sides of the North Atlantic. From this well known plant / centrifuga 
differs by the thicker frond, larger filaments and trichomes, and 
especially by its character of loosening itself from the substratum at 
the centre, while the margin continues firmly attached and growing ; 
sometimes the older parts are broken away leaving only a ring. 
PLEUROCAPSA crepidinum, n. sp. Cells spherical or by mutual 
pressure polygonal, up to 15 p diameter; cell wall rather thin, trans- 
lucent, contents dull blue or slate color. Cells dividing vegetative- 
ly, often remaining attached in dense masses; sporangia spherical, 
filled with small spores. 
This considerably resembles P. amethystea Rosenvinge, Grønlands 
Havalger, p. 968, fig. 57, and it was at first supposed to be that spe- 
cies ; but Dr. Rosenvinge, to whom a specimen was sent, pronounces 
it distinct. Z. amethystea has a lilacor violet color, and less regular 
sporangia, the formation of the spores seeming to be rather the 
