2S FRESn-WATER A L G ,E OF THE UNITED STATES. 



provided with distinct broad browiiisli sheaths : every gradation exists between 

 tlicsc forms and the tirst described fronds. The heterocysts are quite uniform iu 

 size, agreeing in diameter with the largest vegetative cells, they are always single. 

 This species is most nearly allied to N. ichthyoon, Kabenh. ; from which it is 

 separated by the differences in the sheaths, the greater size of the filaments, and 

 the m\"\e heterocysts. It gives me great pleasure to dedicate the species to Mr. 

 Austin, by whom it was collected near Gloucester, New Jersey, growing amidst 

 mosses on rocks. 



I¥. priiiiirorine, (Roth,) Agh. 



N. magnum, gregarium, noncohaerens, globosum, magnitudine pisi, pruni majoris et ultra, oliva- 

 ceum vel saturate serugincum, rotate provecta fusco-nigrescens, baud raro cavum, lajvissiraum, 

 iutus aquosum, peridermate eoriaceo subacbroo ; tricbomatibus subEequalibus, liic illic tumidis, 

 lase iutricatis; articulis globosis, plerumque compressis, saspe didymis, arete connexis; cel- 

 lulis perdurautibus articulis duplo majoribus, plerumque terminalibns, rarius iuterjcctis. R. 

 Species mibi ignota. 



Z)/a??i.— Artie. 0.00024"— 0.0003" ; cell, perdur. 0.0003—0.00045". (R.) 



Syn. — N. pruniforme, (Roth,) Ag. Rabenhorst, Flora Europ. Algarum, Sect. II. p 108. 



Eab. — Maine. Leidy. 



Large, gregarious, not cobering, globose, varying from the size of a pea to a large plum, or 

 even beyond this, olivaceous or deep serugineous, in old age blackish fuscous, often hollow, 

 very smooth, within watery, periderm coriaceous, somewhat transparent; filaments subequal, 

 here and there swollen, laxly intricate; articles globose, mostly compressed, often twofold, 

 closely connected; heterocysts twice the size of the vegetative cells, mostly terminal, rarely 

 interspersed. 



Bemarks. — 1 have never found this species ; but some years since some speci- 

 mens, sent to the Academy of Natural Sciences of Philadelphia from Maine, were 

 identified by Professor Joseph Leidy as belonging to it. 



IV. Temicosiiiu, (Linn.) Vauch. 



N. magnum, gregarium, bipollicare et ultra, subglobosum, soepe lobatum, verruculosum, irrora- 

 tum, initio soliduni, postremo cavum, vesiciforme, saturate brunneo-viride ; peridermate mera- 

 branaceo-coriaceo, olivaceo-fuscescente; tricbomatibus varie curvatis, centralibus parcioribus 

 et laxissime intricatis, peripbericis densius intricatis; articulis oblongis, rare globosis, arete 

 connexis, crassc granulatis ; cellulis perdurautibus interstitialibus vel terminalibus, sphajricis, 

 articulorum diametro duplo majoribus. 



Diam.— Cell vegetativ. .000166"; cell, perdurant. .000233". 



Syn.~N. verrucosum, (Linn.) Vauch. Rabenhorst, Flora Europ. Algarum, Sect. IL p. 176. 



Eab. — In fonte. Centre County, Pennsylvania. 



Large, subglobose, often lobed, warty ; gregarious, two inches in diameter, growing under water, 

 fixed, in the Ijcgiuning solid, afterwards hollow, bladder-shaped; periderm membranaceous, 

 coriaceous, olivaceous-fuscous; filaments variously curved, centrally fewer, and laxly intricate, 

 towards the outside much more close; articles oblong, rarely globose, closely connected, 

 coarsely granulate; heterocysts interstitial or terminal, spherical, twice the size of the other 

 joints. 



RemarJcs.—ln the summer of 1869, 1 found a nostoc growing in great abundance 

 in a very cold, large, limestone spring in Centre County, Pennsylvania, which I 



