THE MAKINE ALGiE OF NEW ENGLAND. 39 



])receding species in liaving filaments .DOS'""' to.Ol-J""" in ilianutcr, was recoj^nized by 

 Dr. Boniet in ct>nii»any with li. plirata in a specimen from Cohasset Narrows. As wc 

 have not been able to recoj^nize the species in any of our own specimens from the 

 same locality, the presumption is that it is not very common. 



ISACTIS, Tlmret. 



(From lonr, eijual. and aKnr, a ray.) 

 Froiul plane, composed of parallel lilaiiients, held together hy a toiigli, 

 uehitiiious iutercelhdar substance, ending in a hyaline hair, hetero- 

 ( ysts basal, ramifications few. Spores unknown. 



This genus ditlera from liicnlana only in that the lihimmts are jiaralbl t(» ono 

 another so as to form a llat frond, whereas in IHntlarid they radiate from a central 

 jMiint and ft)rm more or less spherical fronds. It mi^Mit with pr<»iiriety be considered 

 a subgenus under liivularia. 



I. PLANA, Thnret, 1. e. {JJasi/actisj Kiitz. — Physactis atropurpurea, 

 ohducens, Kiitz.) PI. I, Fig. 2. 



Frond llat, thin, dense, dark green, outline irregular, lilaments 



.OOTtUOj '"in diameter, .12-.15"'"'high sheaths often torn and .striate. 



Whole Xew England coast; Europe. 



Very common on rocks, Fucua, Punciaria, and other algip, forming dark-green spots, 

 scarcely raised above the substance on which it is growing. 



• HOmrACTIS, Thuret. 

 (From upfio^, a necklace, and uktic, a ray.) 



Frond gelatinous, globose, at first solid, then hollow and plicate, 

 lieterocyst intercalary, filaments simi)le at the surface of frond, bifur- 

 cating below. Spores unknown. 



II. QuoYi, (Ag.) Bornet, in litt. [Rividaria nithla, Farlow, List of 

 Marine Algie, 1870. PI. II, Tig. 1. 



Fronds gregarious, dark green, i)licato-rugose, from a quarter of an 

 inch to two to three inches in diameter, filaments .0028-55""" in diam- 

 eter, tortuou.s, cells of external part of the frond thick and discoidal, 

 becoming more oval in the interior of the frond heterocysts numer- 

 ous, scattered, about .0038'""' x .0058""'". 



Exs. — Alg. Am. Bor., Farlow, Anderson & Eaton, Xo. 45. 



Wood's IIoll, Mas.s., W, G.F.; Falmouth, ^lass., Mr. F. S. Collins; 

 Marianne Islands. 



This interesting species, although it has as yet only been found at Woutl's Hull and 

 the adj«»ining coa.st, will probably also be found at other localities on Long Island 

 .Sound. It grows in considerable quantities upon species of Fucus, at half tide, on the 

 inner side of Parker's Point, Wootl's Holl, and we have also fountl it washed asboro 

 on the b«*aches of Btizzard's Hay, in the same township. It nuikes its appearance in 

 June, and disappears in the month of September, being in perfection in the month of 

 July. The fronds sometimes ac<iuire a large size, two or three inches in dianu-ter, 

 but usually they are much smaller and densely aggregated, almost covering the Fucus 



