8 The Rev. W. Smith on the Diatomacese. 



are indications in the front view of the other three species I 

 have figured to warrant the conclusion that these valvular ap- 

 pendages are more or less perfectly developed in their cases, 

 though the minuteness of their frustules prevents their certain 

 recognition. It is only on an end view of the valve that the alee 

 can be clearly seen ; this is not often obtained ; but I have several 

 specimens of S. hisei'iata mounted in balsam showing the end 

 view as figured in PI. II. fig. 1 d, where these remarkable pro- 

 longations of the valves are singiilarly conspicuous. The section 

 given in same plate, fig. 1 e, shows that the position of the wings 

 is such, that they cannot be detected on a lateral view, as they 

 stand up nearly at right angles to the plane of the valve. 



The costje so conspicuous in several species, as well as in Cam- 

 jiylodiscus costaius and sjnralis, appear to be caused by canals or 

 tubes passing between the siliceous valves and the inner mem- 

 brane of the cell ; these canals communicate with the exterior by 

 a series of perforations (PI. II. fig. 1^) along the suture or line 

 where the connecting membrane unites with the valves. Accept- 

 ing the Diatom as a vegetable organism, these tubes will be re- 

 garded as analogous to the intercellular passages, and the exterior 

 ])erforations will perform the office of the stomates of the leaf. 

 In S. biseriata and splendida the costse or undulations caused by 

 these tubes are continued to the margins of the alje, and give a 

 singularly beautiful appearance to the front view of the frustule, 

 as seen in PL II. fig. 1 6 & fig. 3 b. 



Surirella biseriata, De Breb. Frustule on fi-ont view linear ob- 

 long, extremities rounded ; on side view elliptico-lanceolate, 

 extremities acute ; alse large, costse conspicuous. Average 

 length of valve y j^ of an inch, greatest breadth of ditto ^^^ of 

 an inch {v. v.). 



Naricula hifrons, Ehr. Infus. 1838. Surirella hifrons, Ehr. 1843; 

 Kiitz. Bacill. p. 61. tab. 7. %. 10, tab. 28. fig. 29; Phy. Ger. 

 p. 71. Surirella biseriata, De Breb. Alg. Falaise, 1835 ; Hassall, 

 Brit. Freshwater Algse, p. 438. pi. 102. fig. 1 ; Kutz. Sp. Alg. p. 37. 



Freshwater. Living: Wareham, 1847. Lewes, 1850. Fossil: 

 Lough Mourne deposit, described in 'Ann. Nat. Hist.' Feb. 1850. 

 Peterhead, Aberdeenshire, described by Br. Dickie, ' Ann. Nat. Hist.' 

 August 1848 ! In earth from Dolgelly, N.W., sent me by Chr. John- 

 son, Esq. ! 



This species is frequently to be met with in ditches and ponds 

 mixed with Oscillatoriea, &c. ; when occurring alone it forms 

 a brown stratum at the bottom of boggy pools. It is one of 

 the most beautiful of the Diatomacea. Its elaborate form 

 would seem to imply a structure more complex than that of a 

 single cell, yet its mode of self-division is })erfectly similar to 

 that of the simplest of the tribe. In living specimens I have 



