The Rev. W. Smith on the Diatomacese. 13 



This species varies veiy much in size, and in the form of the 

 extremities of the valves, which are either attenuated, rounded 

 and obtuse, or furnished with apiculi, as in PI. III. fig. 8 ; the 

 latter appendages however generally occur in the younger or at 

 least smaller specimens. 



Platk III. fig. 9. C solea, front and lateral view of a mature frustule ; 

 fig. 8. front and lateral view of a young (?) frustule. 



Cymatopleura elliptica, mihi. Frustule on front view oblong, 

 linear, on side view broadly elliptical ; svu'face of the valve 

 with about four undulations, obscurely striated. Length of 

 valve from 3 j^ to ^^0 ^^ ^^ inch, breadth of ditto about half 

 the length [v. v.) . 



Surirella elliptica, Kutz. Bacill. p. 61. tab. 28. fig. 28 ; Sp. Alg. 

 p. 37. 



Widely but sparingly distributed in slow streams or ponds mixed 

 with Oscillatorieee. Living: river Froome near Dorchester. "Brooks" 

 near Lewes. Bramley near Guildford, J. R. Capron, Esq. ! Fossil : 

 in Peterhead deposit, Dr. Dickie ! Lough Mourne deposit ; Dolgelly 

 earth ! 



Very variable in size, the fossil specimens being usually twice 

 as large as the recent frustules, but intermediate forms fre- 

 quently occur. In Kiitzing's description and figure of S. elliptica, 

 one extremity is represented as larger and rounder than the other ; 

 I have not been able to verify this peculiarity, but observe in 

 the larger forms, and occasionally in the smaller, that both extre- 

 mities of the valves are somewhat pointed. 



Plate III. figs. 10 & 11. C. elliptica, front and lateral views of fossil and 

 recent frustules. 



Cymatopleura Hibernica, mihi. Frustule on side view orbicular, 

 with prominent, somewhat pointed extremities ; surface of the 

 valve with about three undulations, obscui-ely striated. Length 

 of valve from yf^ to -^^-^ of an inch, breadth about |rds of the 

 length {v. s.). 



In a slide labelled " River Bann, Ireland," from Mr. Cocken of 

 Brighton ! 



Unfortunately none of the frustules occm-ring in the slide 

 above mentioned present a front view of this interesting species. 

 The single valves, which are numerous, are however so distinctly 

 allied to the last species, that I do not hesitate to place them 

 under the present genus. 

 Plate III. fig. 12. C. Hibernica, side view of a valve. 



The above must not be regarded as a complete monograph of 

 the British species of the genera described, but be taken as a 



