for the Microscope. 37 



261. BLUNT NITZSCHIA (Nitzschia virgata). This is 

 also straight in the front view, with the valves slightly 

 curved, and obtuse at the extremities. The distinct striae 

 become dilated into bands towards the margin. Common 

 in gatherings from sand ripples. 



262. INFLATED SYNEDRA (Synedra ftilgens). In this 

 genus the frustules are long and attached by the lower 

 end. In the present species they grow at the extremities 

 of a thick branched stem, and the valves are inflated at 

 the middle and ends. Found attached to seaweeds. 



263. ACUTE SYNEDRA (Synedra affinis). Grows in fan- 

 like tufts at the extremity of a stem. The valves are 

 acute and spear-shaped. Also parasitic on seaweeds. 



264. SLENDER TRYBLIONELLA (Tryblionella gracilis). 

 This genus is allied to Surirella, from which it is distin- 

 guished by its more regular and symmetrical form, and 

 parallel, scarcely conspicuous, canaliculi or channels. 

 Found in brackish water. (PI. IV., fig. 24.) 



265. COMMON TRYBLIONELLA (Tryblionella acuminatd). 

 The valves in this species are linear, with pointed ends 

 and interrupted strise. Very common in brackish water. 



266. WINGED SURIRELLA (Surirdla striatula}. In this 

 genus the frustules are usually somewhat wedge-shaped, 

 the margins produced into a kind of wing, with distinct 

 and usually parallel channels. The valves of the present 

 species are ovate and striate, and somewhat resemble the 

 next species. Found in brackish water. 



267. FINE-RIBBED SURIRELLA (SurireUa gemma) has 

 much finer ribs than the last, with a less conspicuous wing, 

 and is finely striate between the ribs (costse). Occurs 

 also in brackish water. 



268. OVAL SURIRELLA (Surirella ovalis). A small 

 form, attenuated towards one extremity, and the margin 

 with short teeth-like ribs. The centre of the valve is 

 striate. 



269. DOITED CAMPYLOTuscus(Camfl}>fodis<:us cribrosus). 

 As Smith has observed, the "species included under 

 this ge-nus may all be recognized by the characteristic bend 

 or contortion of their surfaces," This species has. an ob- 



