496 DESCRIPTION OF [^Polygastrica. 



The lorica is incombustible, but the mantle is not. Two openings 

 only are seen, these are central. In some a canal seems to run from 

 one end to the other. Granular contents yellowish-green. 



This genus is not recognised by Kiitzing, who distributes its 

 members chiefly with Schizonema. 



Naunema Amphioxys. — Navicular bodies small, linear-lanceolate, 

 acute, smooth, densely grouped in bundles. Mexico, in fresh water (r). 

 A very doubtful species, says Kiitzing (P. 15, f. 55, 56, 57). 



N. Americanum. — Very large, sub-acute, linear, aggregated in 

 branched dense tubules; striated, eighteen striae in 1-1 152nd. 

 Length l-192nd. Alive in the Hudson, N. America. 



N. simplex f Shizonema, Ag.) — Lorica oblong, rounded at the ends, 

 and smooth, resembling N. arluscula. IsTaviculiB (frustules) disposed 

 in a simple series within flexible filiform tubes. Found upon Cera- 

 mium hyalinum, and other sea- weed. Length 1-1 150th to 1 -570th. 



N. DiUwynii^^ Scldzonema Elirenbcryii (Kxitz.) — Naviculae oblong, 

 small, rounded ujjon the dorsal and ventral surfaces, and densely 

 arranged in many series, within simple branched tubes; always 

 firmly attached. In salt water. Length l-2300th to 1-1 150th. 



N. Hoffmanni. — IS'aviculse small, smooth; numerous and dense 

 within branched tubes. Found in brackish water. Length 1-1 150th. 



N. Arbuscula. The tree- like Naunema. — J^aviculas robust, striated ; 

 numerous and dense, within erect fruticose tubes. Length l-860th. 



N. Balticum. — Naviculae long, narrow, striated. Fig. 207 repre- 

 sents a portion of a gelatinous tube, suiTOunding several. They are 

 numerous and dense within flexible branched tubes, Avhich are tufted. 

 In salt water. Length l-860th. 



Genus EHAPHiDOGLffiA (Kiitz.) — Phycoma (thallus), globose, gela- 

 tinous, soft ; its substance filled by bundles of navicular bodies, dis- 

 posed in radiating threads. 



This belongs to Kiitzing's great family Naviculeoi, and to its sub- 

 section Schizoneniece. 

 All the species are marine. 



R. medusina. — Small, fasicles lanceolate, acuminate, radiating in 

 ii'iregulurly reticulate or bruuchod threads ; naviculae lanceolate. 

 Length 1 -600th. Diameter of frond l-12th. 



