FRESH-WATER ALG^ OP THE UNITED STATES. 21 



Hah. — In stagnis prope Philadelphia. 



0. occurring in an olive-blaclc, mucous stratum, mostly swimming and with long rays ; filaments 

 straight or straightlsh, light-green or deep-olive, tranquil, not oscillating, but moving with a 

 gliding motion ; ends somewhat attenuate, broadly rounded or subtruncate, curved ; articles 

 5-12 times shorter than broad, slightly contracted at the joints; cytioplasm homogeneous, 

 olive-green ; sheaths firm, distinctly transversely grooved at the joints. 



Remarks.— The strata of this species are often of great extent, and resemble 

 more masses of spirogyra than of the ordinary oscillatoria. They are very loose in 

 texture and are very slimy, whilst their edges are fringed by the long tranquil 

 rays. In certain conditions of growth, the endochrome of the filaments is so dense 

 as to render them very opaque and the articulations very obscure. The sheaths 

 when emptied show the marks of the joints very distinctly ; but, at times, when 

 gorged with cytioplasm, scarcely can the sheath itself be seen. The color of the 

 filament is also affected by the state of the protoplasm, so that it varies from a 

 lightish-green with an olive tint to a very decided dark olive. This species seems 

 to be closely allied to the European 0. princeps, from which, however, it differs in 

 its motion, which is always very slow and merely gliding, its color, the distance of 

 the dissepiments, and the much longer curvature of the ends. It grows everywhere 

 in the ditches around the city ; when mature, generally floating upon the surface 

 with an adherent undei'-stratura of dirt, but, in its earlier history, often adhering 

 to the bottom. * 



Fig. 6a, pi. 1, is a drawing of the end of a filament; fig. 65, represents a small 

 fragment of a filament, showing the tendency to take a roundish or barrel shape; 

 ftiuch of the endochrome has been squeezed out by the injury which has broken 

 the filaments. 



Genus CHTHONOBLASTUS, Ktz. 



Phormidii trichomata fasciatim congesta et vagina communi mucosa apice clausa vel aperta inclusa. 

 Tales fasciculi numerosi in stratum (quasi thallum) gelatinosum, passim amoso-divisum aggregati. 

 Vaginse communes achromaticae, saepe lamellosse, plus minus ampliatse, rarius indistinctas et subnullae, 

 evacuatse, plerumque valde intumescentes. Trichomata Phormidii modo oscillantia, articulata et 

 vaginata, rigida, recta vel parum curvula, in fascicules funiformes plus minus dense contorta, apice 

 soluta et divaricata. Cellulas prbpagatorias observare mihi contigit. (R.) 



Filaments fasciately placed together and included in a common mucous sheath with open or shut 

 apex. A number of these fasciculi aggregated in a gelatinous stratum (pseudothallus), which is 

 gelatinous, and here and there ramosely divaricate. Common sheath colorless, often lamellate, more 

 or less enlarged, rarely indistinct and nearly wanting, when empty mostly markedly intumescent. 

 Filaments oscillating like to those of Phormidium, articulate and vaginate, rigid, straight, or a little 

 curved, more or less densely entangled into cord-like fasciculi, with the apex dissolved and dis- 

 severed. 



Ch. repens, Ktz. 



Ch. terrestris, strato plus minus expanso, saturate Dsrugineo-chalybeo aut olivaceo-fuscescente, 

 mucoso-membranaceo ; tvichomatibus sequalibus in fascicules filiformes, ssepe valde elon- 

 gates, e vaginse communis apertura penicillatira exsertos cengestis ; articulis diametro eequali- 

 bus dissepimentis granulatis, apicnlo obtuse recto. (R.) 



Species, mihi ignota. 



