FRESH-WATER AhGM OF THE UNITED STATES. 31 



subovalibus, arete connexis; cytioplasmate granulate; cellulis perdurantibus interjectis 

 terminalibusque, sphsericis. 



Diam— Artie, diam. long. -g^Vir" = -000125" ; transv. ^^Vtf" = -OOOIT"; cell, perdurant. 

 WW = -00029". 



Syn. — N. sphsericum (Poiret ) Va€ch. Rabenhorst, Flora Europ. Algarum, Sect. II. p. 16T. 



Hab. — In fontibus, prope PhiladelJ)hia. 



Globose, sometimes oblong or oval, gregarious, but rarely confluent, Lard, elastic (in advanced 

 age within soft and watery?), olivaceous, varying from the size of a mustard-seed to that of 

 a small cherry; periderm firm, pellucid; filaments intricate, yellowish, greenish or bluish; 

 articles mostly subquadrate, sometimes transversely suboval, closely connected ; cytioplasm 

 granular ; heterocysts interspersed or terminal, spherical. 



Bemarks. — The specimens from which the above diagnosis was prepared were 

 found at Spring Mills, adhering to mosses and twigs in the water. The fronds 

 were remarkable for their firmness and elasticity. The color was a dull, rather 

 greenish, olive ; that of the filaments varied from a decided greenish to a marked 

 yellowish, or sometimes an almost silvery bluish tint. The heterocysts were rather 

 few in number, and were either terminal or interstitial, sometimes they were with- 

 out, sometimes with evident endochrome. The length of the general articulations 

 varied a good deal, it was, however, mostly less than their breadth, which seems 

 quite constant. When kept in water in the house, this species softens, and the 

 periderm as it were peels off, allowing the interior to disperse itself as it gradu- 

 ally becomes more and more diffluent. Most of the fronds afforded ample evidence 

 of theij method of' growth by the presence of filaments in every stage of division. 



Fig- 10, pi. 2, represents filaments of this species. 



]¥. caBruleum, Lyngb. 



N. minimum, ssepe microseopicum, enormiter globosum vel subglobosum, af&xuta, gregarium, 

 sejunctum vel aggregatum ; triehoraatibus valde insequalibus ; articulis elongato-eylindraceis, 

 vel acute ellipticis, vel perfecte elliptieis, vel globosis, vel subglobosis, vel subquadrangulis, 

 sejunctis et nonnihil distantibus vel arete connectis aut confluentibus ; cellulis perdurantibus 

 globosis, passim interjectis terminalibusque, ceteris duplo vel subduplo majoribus. 



Diam.—CeW. perdurant, .000303; cell, vegetat. plerumque .00012—000166"; rarius .0001— 

 .00021. 



Syn. — N. cxruleum, Lyngb. Rabenhorst, Flora Europ. Algarum, Sect. II. p. 1 eT. 



Eab. — Inter muscos. New Jersey (Prof. Austin). 



Tery small, often microscopic, irregularly globose or subglobose, affixed, gregarious, separate or 

 aggregated ; filaments very unequal ; articles eldngate-eylindrieal, or acutely elliptical or 

 perfectly so, or subglobose, or globose, or subquadrangular, separate and somevirhat distant 

 or closely connected or confluent ; heterocysts globose, interspersed or terminal, double or 

 about double the size of the other cells. 



Remarhs. — I am indebted to Mr. Austin for specimens of this species collected by 

 him in Northern New Jersey. The fronds grow attached to moss and are very mi- 

 nute, the largest I have seen being not more than half a line in diameter. The 

 filaments are remarkable for their inequality, which is often very perceptible in 

 different parts of the same filament. I have referred my specimens to N. cwruleum— 



