with descriptions of new genera and species. 1 69 



Ortkoseira Dickieii was kindly communicated to me by Dr. 

 Dickie, who discovered this beautiful species in December last 

 near Aberdeen in a moist dripping dark cave close by the sea, 

 and covering the Mosses, Hepaticse, &c. as a fine blackish green 

 sand, collecting also in the shelvings of the rock. 



Cyclotella? Kiitzingiana, n. sp. PI. XI. fig. D 1-5 (^-). Cel- 



lulis latere primario sigmoideo-flexuoso, lateribus secundariis 



radiatim striatis. 



The frustules of this species, fig. D 1, 2, are short, and exhibit 

 an apparent sigmoid curvature, which is due to each of their stri- 

 ated disciform ends having a prominence on one side of its centre 

 and a depression on the other, and the opposite end of the frus- 

 tule having a depression and prominence corresponding to these. 

 The sporangia, fig. D 3, 4, are developed much "in the same way 

 as in Meloseira. This species is evidently closely allied to Cy- 

 clotella ? minutula, Kiitz. Bacill. tab. 2. fig. 3, but differs in the 

 fewer number of curvatures apparent in the frustule. The spo- 

 rangial frustules, fig. D 5, are very similar to Cyclotella ? Rotula, 

 Kiitz. Bacill. tab. 2. fig. 4. A species of Cyclotella collected by 

 Geo. Dansey, Esq. near Devonport, and which I suspect may be 

 the C. operculata of Kiitzing, differs from the present species in 

 the radiating strire being only slightly marked, and in the curved 

 appearance of the frustule being scarcely evident. 



Occurs in brackish ditches amongst the leaves of Myriophyl- 

 lum, &c. Wareham, llev. W. Smith ; Shirehampton near Bristol, 

 G.H.K.T. 



Before taking leave for the present of the Meloseirece, I cannot 

 avoid referring to the analogy they offer to the genus Tiresias, 

 Bory (QLdogonium, Link, Vesiculifera, Hassall), and its allies. 

 The Meloseirece seem to bear the same relation to these that the 

 other Diatomacece do to the Conjugates. The annulated struc- 

 ture of the sporangium of Ortkoseira also recalls to mind and 

 explains the character of the rings which are met with at the end 

 of the fructifying cell in Tiresias. 



Schizonema eocimium, n. sp. PI. XII. fig. F 1 (-[-), 2, 3, 4 (— ). 



Cselomatibus simplicibus aut parce ramosis, rugulosis : navi- 



culis sigmoideis lsevibus. 



The sigmoid frustules of this beautiful freshwater species at 

 once distinguish it from any other described Schizonema. The 

 delicate gelatinous sheaths are simple or very sparingly branched 

 and minutely rugulose, especially near their base ; they contain 

 from one to four rows of the large, smooth, sigmoid frustules. 



