THE MARINE ALG^ OF NEW ENGLAND. 37 



easily distinguished under the microscope, C. confervicola being darker colored, the 

 .filaments thicker, and only furnished with heterocysts at the base, whereas in 

 C. Crustacea the heterocysts are scattered through the filament, often solitary, but 

 sometimes as many as eight together, and frequently truncate. C. Crustacea is also 

 common on rocks. 



b. Species forming expansions. 



C. scopulorum, Ag., Phyc. Brit., PI. 58 b; Xer. Am. Bor., Part 

 III, p. 105. 



Eilaments forming strata of indefinite extent, flexuous, usually 

 branching, .00S-12 mm in diameter, heterocysts basal and intercalary, 

 sheaths thick, striate. 



Var. vivipara. (C. vivipara, Harv., Ner. Am. Bor., Part III, p. 10G.) 



Valiant, Wood's Holl, Mass., W. G. F. ; Bhode Island, Bailey; Eu- 

 rope. Var. vivipara at Nahant, W. G. F., and Seaconnet Point, Bailey. 



Forming indefinite-shaped patches on rocks, on RMzoclonium, and other prostrate 

 alg?e. Apparently much less common tban the two preceding species. It differs 

 from C. Crustacea in the flexuous habit of the filaments, which are loosely twisted 

 around one another, in the much rarer occurrence of intercalary heterocysts, and in 

 the color of the filaments, which is not a bright green, but generally brownish. The 

 sheaths, too, become thick, dark, and striated. As is the case in all species of Calo- 

 th/rix where the filaments are closely interwoven, the diameter of the filaments is 

 greater and that of the sheath less, proceeding from within outwards. The variety 

 vivipara is only a luxuriant form of the typical species. 



C. pulvinata, Ag. (C. hydnoides, Harv.) 



Filaments densely packed, forming a dark-green spongy layer, united 

 at the surface in tooth-like masses, flexuous, .006 mm to .0115 mm in diam- 

 eter, heterocysts intercalary. 



Exs. — Alg. Am. Bor., Farlow, Anderson & Eaton, No. 50. 



Wood's Holl, on wharves. Common. Europe. 



Iu this species the filaments are much more densely interwoven and flexuous than 

 in any of the preceding species. It forms patches looking like a honeycomb, or like 

 a small Hydnum, and can be torn from its attachment in pieces of considerable size. 



G. parasitica, Thuret. (Bivularia, Chauvin. — Schizosiphon, Le Jolis.) 



Filaments loosely united, forming a velvety film, bulbous at base, 



simple or only slightly branching, about .008-1 mm in diameter, 



heterocysts basal, obliquely truncate. 



On Nemalion multijidum, Newport, R. I. ; Europe. 



Easily recognized by its bulbous base and obliquely truncate heterocysts, aud its 

 peculiar habitat. 



RIYULABIA, Both. 

 (Named from the fluviatile habitat of many of the species. ) 



Frond gelatinous, more or less globose, filaments radiating, atten- 

 uated, furnished" with distinct sheaths, branching, a heterocyst at the 

 base of each branch. 



