Mr. J. Ralfs on the British Diatomacese. 109 



Puffinus anglorum. 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. I 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 : seen on the salt lake only 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 Diatomace^. By John Ralps, Esq., 

 M.R.C.S., Penzance*. 



[With a Plate.] 



HOMCEOCLADIA, Aff. 



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, Hoxy. 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 oiH.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 in 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 

 simple or once dichotomous, or occasionally trichotomous. The 

 extremities are often clavate, but not unfrequently slightly 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. 



