BRITISH DIATOMACEyE. 77 



9. Schizonema Grevillii, Ag. Frond filiform, much divided from 

 the base; ultimate ramuli acute; larger divisions with several 

 files, ultimate ramuli with a single file of frustules ; valve lanceo- 

 late; striae 60 in -001". Length of frond -5" to 1*5". Length of 

 frustule -0017" to -0025". Breadth of valve -00055". v.v. 



Ag. Consp. p. 19. ad specimina authentica in herb. Grev. Grev. B. F. p. 413. 

 Schizonema quadripunctatum et S. Grevillii, Harv. Man. p. 214. ad 

 specimina authentica. S. Grevillii, Kiitz. Bacill. v. 1. & xxvi. 4. ad 

 specim. quse dedit cl. De Brebisson. Bangia quadripunctata, Lyng. 

 Tent. 26 ? 



Marine. Torbay, Mrs. Griffiths and Mrs. Wyatt. Pevensey Bay, Sussex, 

 Sept. 1850 and May 1852 ; Hove, Sussex, March 1851, W. Sm. Saltcoats, 

 March 1854, Dr. Arnott. Frith of Forth, Br. Greville. 



The large, and on the F. V. nearly square frustules of this remarkable 

 species are not likely to be confounded with those of any other Schizonema, 

 and enable me to give the above synonymy with tolerable confidence. 



Plate LVIII. 364. 



10. Schizonema molle, n. sp. Frond gelatinous, simple below, 

 membranous by cohesion above ; margin much divided into acute 

 segments ; frustules in crowded files ; valves lanceolate, acute ; 

 stria? 48 in -001". Length of frond -6". Length of frustule -0012" 

 to -0015". Breadth of valve -00045". v.s. 



Marine. Coast of Aberdeen, 1847, Br. Bickie. Exmouth, July 1854, 

 Miss Cutler. 



I cannot reduce this species to any of the previous, nor to any form given 

 in Harvey's ' Manual.' The frustules are very like those of S. helmintosum, 

 but the form and structure of the frond are altogether different : in general 

 character, the frond belongs to the next section, being soft and flaccid, but the 

 frustules are firmly siliceous, and resist the action of acid. 



Plate LVIII. 365. 



Sect. II. Frustules imperfectly siliceous ; striae obscure ; frond 



flaccid. 



11. Schizonema Dillwynii, Ag. Frond capillary throughout, 

 sparingly branched, tenacious, apices acute ; frustules exceedingly 

 crowded towards the apices, scattered and remote in the older 

 portions ; valves lanceolate, acute. Length of frond 2" to 5" or 



