| My. J. Ralfs on the British Diatomacese. 109 
Puffinus anglorums A few seen.) 
Thalassidroma pelagica: Very common : breed. 
‘Cygnus: musicus. A few seen in the lakes of Biserta, and one in 
the lake of Tunis. 
Anas Boschas. Common: breed in the marshes round. Biserta. 
A. marmorata. -1 only saw two small, flocks of five. or six each 
flying up the river between the lakes; one of these very rare birds I 
was fortunate enough to procure ; it proved to be a female. 
A. Fuligula.. Very numerous: scen on the salt lake on/y,in large 
flocks of two or three hundred ; it is singular that they should be in 
flocks so late in the season. 
Pelecanus onocrotalus, A few seen.on the salt lake. 
Carbo Cormoranus. Very numerous on both lakes. 
XII-—On the British Diatomacer. By Joun Rarrs, Hsq., 
M.R.C.S., Penzance*. 
: [ With a Plate. ] 
Hommoc.apia, Ag. 
Frond membranaceous, tubular, filiform, transversely wrinkled, 
branched in an umbellate manner ; frustules linear. 
1. H. anglica, Ag. Fronds umbellate at the base, above elongated 
and either simple or dichotomous ; frustules. linear, many times 
longer than broad, with striated lateral surfaces. Ag. Consp. 
Diatom. p. 25; Harv. Br. Alg. p. 208; Kiitz. Die Kieselschaligen 
Bacillaria oder Diatomeen, p. 110. tab. 30. fig. 82... Oscillatoria 
chthonoplastes, Harv. in Hook. Br. Fl. vol. ii. p.373. Microcoleus 
marinus, Hary. Br. Alg. p. 168. 
On marine rocks, Ilfracombe, and Petitor near Torquay, Septem- 
ber and October. 
Since my former note on this plant (Ann. Nat. Hist. vol.xi. p.77) 
I have examined specimens in a fresh state, and find its structure 
agrees so closely with Agardh’s description of H. Martiana, that the 
difference appears to be but slight. It is brownish when recent and 
becomes of an opake olive-brown when dry, and often acquires a 
metallic lustre, particularly in the Torquay specimens. _ It arises 
from a comparatively thick scutate base, but soon divides. m an 
umbellate manner into many branches, each of which. is again 
similarly divided. In this second division the branches, which 
vary in number from three to five, are elongated, and are either 
sunple or once dichotomous, or occasionally trichotomous... The 
extremities are often clavate, but not unfrequently shghtly at- 
tenuated. The frond, which is from one to two inches high, is 
terete, erect, tubular, with numerous transverse but irregular 
wrinkles, which produce a crenated appearance of the margin. 
* Read before the Botanical Society of Edinburgh. 
