78 ALG.E. 



ting lines, with intermediate rows of dots these 

 markings being continued over the margins of the 

 valves so as to appear also in the front view (fig. 30/), 

 ceasing at the hoop. The frustules are curved or 

 arcuate (ar'cus, a bow) in the side view, oblong and 

 narrowed at the ends in the front view. 



In Fragildria capucina (PL V. fig. 23), which is ex- 

 tremely common in fresh- water pools, &c., the frus- 

 tules are united side by side into long filaments, 

 which are often twisted. In the separate and pre- 

 pared frustule, the front view (PL V. fig. 24/) is rect- 

 angular, the valves (s) being narrowly lance-shaped 

 or lanceolate. The valves under ordinary illumina- 

 tion appear colourless and without markings, but, by 

 proper management of the light, very fine transverse 

 striae are seen upon them, consisting of rows of very 

 minute dots. Fig. 24 s* represents the valve of Fra- 

 gilaria vires' cens, a nearly allied species. 



Diat'oma elongdtum (PL V. fig. 31) is often found 

 with the above. Its frustules are coherent at the 

 angles. The front view (fig. 32 /) is rectangular, 

 often slightly narrowed in the middle ; and the valves 

 are narrowly linear, and capitate at the ends ; they 

 are also transversely striated. 



In Synedra splen'dens {PL V. fig. 5) the frustules 

 radiate from a soft gelatinous cushion. They are 

 linear in the front view (fig. 4 f) , the valves (fig. 4 s) 

 being gradually narrowed or attenuated from the 

 middle to the ends, and exhibit transverse striae 

 interrupted opposite a middle longitudinal line. 



In Campy lodis 'cus costdtus (PL V. fig. 27) the frus- 

 tules are disk-shaped and curved, so as somewhat to 

 resemble a saddle. The markings consist of central 

 dots, with radiating coarse flutings. 



Nitzsch'ia minutis' sima (PL V. fig. 28) has oblique 

 valves, i. e. the front half of the suture is not opposite 

 the back portion ; the valves (fig. 29) are constricted 

 in the middle, and the ends narrowed and prolonged. 



