The Rev. W. Smith on the Diatomacese. 11 



Surirella gemma, Ehr. Frustule on front view wedge-shaped 

 with rounded ends ; side view ovato-elliptical ; alse large ; costse 

 small, unequally distant ; surface of valve distinctly striated. 

 Average length of valve g^^ of an inch, greatest breadth of 

 ditto ^^0 of an inch {v. v.). 



Kiitz. Bacill. p. 62. tab. 7. fig. 9 ; Phy. Ger. p. 72 ; Sp. Alg. p. 38. 



Common on the mud of tidal harbours, &c. Poole Bay, 1847. 

 Belfast Bay, 1849. Shoreham, Seaford, and other places on the 

 Sussex coast, 1850. ^ye,Mr.Jenner\ Shirehampton, near Bristol, 

 Mr. Thwaites ! Hull, Mr. R. Harrison ! 



The costse, which in this species assume the appearance of 

 lines, at once distinguish it from those preceding ; the greater size 

 of the frustule, the irregular disposition of the costse, and their 

 reaching to the central line, separate it from those which follow. 

 The striae may be made out without difficulty on the dry valve 

 after bvirning or maceration in acid : with the parabolic reflector 

 they are very conspicuous, and add much to the beauty of the 

 object. 



It was in connection with this species that Ehrenberg records 

 the presence of cilia, extending from the apertures of the costse, 

 vibrating with rapidity and being extended or retracted at inter- 

 vals ! The presence of delicate hairs, apparently on all parts of 

 the frustule, may often be detected, and I have noticed them on 

 nearly every occasion when I have gathered this species, but in 

 no case have I been able to perceive any motion in such hairs, 

 and concluded, before meeting with Ehrenberg's remark, that 

 they were merely a parasitic growth, the mycelium of some other 

 Algae. I have noticed similar appendages to other Diatomacecp, 

 but in every case devoid of motion. 



Plate III. fig. 2. S. gemma : a, front view of the frustule ; b, side view 

 of ditto ; c, frustules in which self-division is just completed. 



Surirella ovalis, DeBreb. Frustule on front view oblong, some- 

 what cuneate, with truncated extremities ; side view ovate, 

 slightly attenuated at the ends ; alae obsolete or very minute ; 

 costse only visible at the margin of the valves. Average length 

 of valve g ^y of an inch, greatest breadth of ditto y gVo ^^ ^^^ 

 inch {v. v.). 



Kutz. Bacill. p. 64. tab. 30. fig. 64 ; Sp. Alg. p. 38. 



A freshwater species. 'Nea.rBnstol,G. K. Thwaites, Esq. \ "Brooks" 

 near Lewes, 1850. 



Surirella minuta, De Breb. Frustule on fi'ont view wedge-shaped 

 on side view elliptical or slightly ovate, with ends more or less 



