112 My. J. Ralfs on the British Diatomacez. 
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 adleres only imperfectly to paper 
or glass. 
The filaments are short, straight or flexuose, simple or shghtly 
branched, slender, subequal, quite colourless under the micro- 
scope. Generally the frustules form a single series and have 
their convex margin alternately m 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 ashght con- 
striction are usually similar, but m the Ilfracombe specimens one 
of them is often produced into a short beak. A pellucid line 
passes from one to the other and divides the striz 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 Cocconema, the strie slightly converge. 
In the recent frustule the endochrome is tawny with a paler 
transverse band in the centre. 
Kiitzing in his last work deseribes 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. 
Glotonema 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 +. 
Puate III. fig. 3. Eneyonema prostratum: a, front view of frustule ; 
b, lateral view, Sussex specimen ; d, front, and ¢, lateral view of empty frus- 
tules from an Ilfracombe specimen ; e, lateral view of frustules deprived of 
their colouring matter from an original specimen of Monema prostratum. 
* « FE, paradoxum, tubulis sparsis, solitariis ; cymbellis a latere secundario 
acuminatis cornutis striatis. . 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 paradowum, Menegh.” 
+ Annals of Nat. Hist. vol. vii. p. 449. 
