498 DESCRIPTION OF '[Poli/ffastrica. 



Conferva and Vaucheria, but the microscope displays their peculiar 

 and characteristic navicular bodies. 



The closest affinity between these forms and the ordinary Algae 

 exists in the case of Schizonema with Mydrurus ; but the round cor- 

 puscles of the latter are organic like their enveloping mucus, and not 

 siliceous as are the navicular bodies of the former ; a fui-ther differ- 

 ence between the two is to be found in that Schizonema are all marine, 

 and Hyd/rnrus fresh-water habit. 



The following are the peculiarities presented by the gelatinous 

 envelope of the Schizonemece. 



In FrustuUa the investing sheath is gelatinous, and without definite 

 form or outline. In Schizonema, and similar genera, the gelatinous 

 substance forms itself into tubules of determinate form and ramifi- 

 cation ; these tubules containing the naviculae. In Micromega, 

 besides these external tubular ramifications, there are also finer 

 internal tubules, which contain the naviculae, and the entire substance 

 is firmer, more solid, often cartilaginous, like many species of 

 Gigartina, Gelidium, and Sphcerococcus. 



In Dicliieia, the gelatinous matter is developed in a leaf-like form, 

 as a Phylloma or TJiallus, like as in species of Zflvacece. In Encyonema the 

 navicular bodies are different from those of the other Schizonemece. 



KiitzLng affirms, that in Micromega he has seen the naviculae 

 metamorphosed into green globular spores, a most interesting fact, if 

 confirmed. In the ' Species Algarum,' thirty-eight species are given. 



Schizonema minutum. — Parasitic, very short, slender, decumbent, 

 subramose, branches tapering to acute extremities, series few (2 to 3), 

 containing the naviculae, which are acutely lanceolate, or laterally 

 linear. Length of naviculae 1-11 76th ; of the tubes l-36th to l-24th. 

 On marine Algae. 



S. humile. — Parasitic, very short, ccespitose (tufted), erect, sub- 

 ramose ; branches obtuse, hyaline, and naked at the apices ; series 

 few (two to four) ; naviculae linear-lanceolate, acute, laterally 

 linear, truncate; in length 1-12 00th. Length of frond, l-12th 

 to 1-1 0th. 



S. tenellum. — A compact, gelatinous, densely intricate lamina, of 

 a pale green or brown colour ; tubes very slender, colomlcss, hyaline, 



