30 One Thousand Objects 



208. ACUTE FRAGILARIA (Fragilaria capiicinci). The 

 frustules are also quadrangular, narrow, almost line-like, 

 and united into a filament ; whilst the valves are also 

 linear, or narrowly efliptical, and striated. In this species 

 the valves are narrow, with parallel sides and wedge- 

 shaped ends. Common in ditches. (PL III., fig. 31.) 



209. OBTUSE FRAGILARIA (Fragilaria striatula). The 

 valves are broader and their extremities more obtuse than 

 in the previous species, and the striae are much closer 

 together. Common in ditches. 



210. COMMON CHAIN DIATOM (Diatoma vulgare). The 

 frustules are oblong, adhering together by their angles in 

 a zigzag chain. The valves in this species are elliptical, 

 suddenly diminishing at their extremities, and ending 

 bluntly. Attached to confervae growing in gentle streams. 

 (PL III, fig. 32.) 



211. LONG CHAIN DIATOM (Diatoma elongatum}. 

 Longer and narrower than the last, and the valves with 

 straight sides, slightly swollen at the rounded ends ; grow- 

 ing as above, and frequently found living in the water 

 supply of various towns, mixed with the following species. 



212. STELLATE DIATOM (A steriondla formosa). Frus- 

 tules line-like, end swollen, adhering at similar ends, giving 

 a star-like arrangement to the filaments. The filament in 

 this species consists of from four to nine frustules; the 

 adhering end of the frustule is generally rather more en- 

 larged than the free portion. 



213. SIGMOID NITZSCHIA (Nitzschia sigmoidea). In 

 this large group the frustules are not united at any period, 

 and are therefore called free. They are long, narrow, and 

 keeled ; the valves are linear, with punctate margins and 

 transverse lines or striae. In the present species the valves 

 are long and narrow, with parallel sides and short pointed 

 ends. The keel has a single row of dots. Common in 

 every fresh-water gathering. (PL III, fig. 34.) 



214. ARCHED NITZSCHIA (Nitzschia amphioxys). The 

 valves are short, and bent like a bow, with sharp and 

 prominent extremities. The striae are distinct. Common 

 in moss growing in damp situations. (PL IV, fig. 31.) 



