48 BRITISH DIATOMACE./E. 



latter being rather projections from the disk than produced angles. 

 I have given in Plate LXII. fig. 255. front views of Eupodiscus 

 radiatus, which I had not seen when the figure in. Plate XXX. was 

 drawn : the distinctive characters of the two genera, as far as regards 

 the forms and structure of the frustule, may be easily seen on a com- 

 parison of these figures with those of Biddulphia given in the former 

 plate. 



The extremities of the produced angles in Biddulphia appear to be 

 deficient in the distinct cellular structure of the general surface of 

 the valve ; this probably arises from the slighter impregnation of 

 silex at these parts of the cell-membrane, which is occupied for some 

 time after its formation in the secretion of the mucus that retains the 

 frustules in their filamentous connexion. The small amount of silex 

 at these parts often disappears during maceration in acid, or upon 

 exposure to the air, and the result is that the extremities of the pro- 

 cesses appear as if perforated. That openings do not exist at these 

 parts during the life of the frustule, may, however, easily be proved 

 by compressing the specimens under the microscope, when the endo- 

 chrome is seen to escape at the suture, and not by the processes. 



1. Biddulphia pulchella, Gray. Valve elliptical; margin undu- 

 lated, undulations arising from three to seven transverse elevations, 

 the summit of the central elevation armed with two or three abbre- 

 viated, awl-shaped spines, which in the larger specimens are some- 

 times slightly capitate ; elevations of the valve separated by costee ; 

 cellular structure conspicuous ; processes semi-globular. Length 

 of valve -0025" to -0062". v.v. 



Gray, Nat. Arr. of Brit. Plants, vol. i. p. 294. Ralfs, Ann. vol. 12. viii. 3. 

 Prit. Anim. xiii. 46-50. Conferva Biddulphiana, Eng. Bot. tab. 1 703. 

 Diatoma Biddulphianum, Ag. Syst. p. 5. Biddulphia tri-locidaris, quin- 

 que-locularis, et septem-locularis, Kiitz. Bacill. xxix. 89, xix. 1 &xix. 2. 



Marine. Ilfracombe, 1838, Mr. Ralfs. Torquay, 1849, Mrs. Griffiths. 

 Torquay, Aug. 1846 ; Poole Bay, Sept. 1851 ; Cork Harbour, Aug. 1856, 

 W. Sm. Portsmouth, Mr. C. Potdton. Harwich, Mr. Bleakeley. (Cher- 

 bourg, M. Be Brebisson. Mediterranean Sea near Marseilles, May 1854, 

 W. Sm. Mauritius, Dr. Harvey ; communicated by Dr. Arnott. Ceylon, 

 Dr. Harvey ; communicated by Dr. Kelaart.) 



When viewed with a low power of the microscope, as in Plate XLVI. 

 32 \f, no description of this beautiful species can be more graphic than that 

 given by Dr. Greville (Brit. Flora, vol. ii. p. 405) of the form he describes as Dia- 



