112 Mr. J. llalfs on the British Diatomacese. 



crowded as to constitute considerable patches. When recent it 

 is dark brown, but dried it assumes a dull green colour. It is 

 soft, but not gelatinous, and adheres only imperfectly to paper 

 or glass. 



The filaments are short, straight or fiexuose, simple or slightly 

 branched, slender, subequal, quite colourless under the micro- 

 scope. Generally the frustules form a single series and have 

 their convex margin alternately in opposite directions; occa- 

 sionally a frustule is placed transversely, and in the broader fila- 

 ments there are two, or even as many as three or four longitu- 

 dinal series of frustules. 



The frustules are in the front view about three times as long 

 as broad, and slightly rounded at the ends ; their convex lateral 

 surfaces are visible at the sides. 



The lateral view is broader than the front and semi-elliptic. The 

 inferior margin is mostly prominent at the centre. The ends, 

 which are rounded and separated from the body by a slight con- 

 striction are usually similar, but in the llfracombe specimens one 

 of them is often produced into a short beak. A pellucid line 

 passes from one to the other and divides the strise into two un- 

 equal series. There is a dilatation at each extremity of this line, 

 and at the centre a larger one, towards which, as in Gomphonema 

 and Cocconemaj the strise slightly converge. 



In the recent frustule the endochrome is tawny with a paler 

 transverse band in the centre. 



Kiitzing in his last work describes two species of Encyonema^, 

 Judging from his characters and figures, I doubt whether they are 

 sufficiently distinct, as I find that the form of the frustules varies 

 even in the same specimen. 



I have examined an original specimen of Mr. Berkeley's Mo- 

 nema prostratum. The frustules in the lateral view are generally 

 less constricted at the ends than in my other specimens, but 

 they vary in this respect as well as in size. 



Gloionema paradoxum, Ag., which at first sight bears some re- 

 semblance to this plant, has been shown by the Rev. M. J. Ber- 

 keley to be an animal production f. 



Plate III. fig. 3. Encyonema prostratum: a, front view of frustule ; 

 hf lateral view, Sussex specimen ; d, front, and c, lateral view of empty frus- 

 tules from an llfracombe specimen ; e, lateral view of frustules deprived of 

 their colouring matter from an original specimen oi Monema prostratum. 



* " E. paradoxum, tubulis sparsis, solitariis ; cymbellis a latere secundario 

 acuminatis cornutis striatis. E. paradoxum, Kiitz. Syn. 1833. Gloionema 

 paradoxum, Ehr. Inf. Isthmia catenata, Menegh." 



" E. prostratum, stratum gelatinosum formans, tubulis maxime intricatis ; 

 cymbellis minoribus, obtusiusculis non cornutis, striatis. Monema prostra- 

 tum, Berk. Encyonema paradoxum, Menegh.'* 



t Annals of Nat. Hist. vol. vii. p. 449. 



