for the Microscope. 35 



the last, and without a central inflation. Ribs closer than in 

 preceding species. Common everywhere. (PL IV., fig. 9.) 



248. OBLONG PINNULARIA (Pinnularia oblonga). 

 Valve spear-shaped (lanceolate) with rounded ends ; the 

 ribs distant from each other, and reaching to the line down 

 the middle of the valve. Not so common as the above, 

 but frequently mixed with it. 



249. RADIATE PINNULARIA (Pinnularia radiosa). 

 Smaller than the last, of similar form, but more pointed 

 extremities, and the radiate ribs closer together. Common 

 in fresh water. 



250. VARIABLE PINNULARIA (Pinnularia varians). 

 Variable in form and size, with oblique ribs nearly reach- 

 ing the median line, more conspicuous opposite the cen- 

 tral nodule. 



251. BROAD-BANDED STAURONEIS (Stauroneis phcenicen~ 

 teroti). This genus differs from Pinnularia in the central 

 nodule being widened into a clear central band. This 

 species is of a spear-shape (lanceolate). The central band 

 reaches the margin. Striae fine. Very common in all fresh- 

 water gatherings. 



252. DELICATE STAURONEIS (Statironeis gracilis}. 

 Valve of a similar form to the last, but with the central 

 band scarcely reaching to the margin. Strise much closer 

 than in the last species. 



253. NIPPLED STAURONEIS (Stauroneis anceps). Form 

 of the valve elliptical, with teat-like extremities. The 

 central band not reaching to the margin, and the striae 

 delicate. 



254. COMMON PLEUROSIGMA (Pkurosigma lacustre}. 

 The valves in this genus are more or less spear-shaped, 

 with a sigmoid line (like an elongated S) down the middle. 

 This species is of a pale brown colour, and the middle 

 line considerably bent. 



255. NARROW PLEUROSIGMA (Pleurosigma attenuatwn). 

 The colour of this species is purplish brown, the ends 

 of the valves blunt, and the median line less waved than 

 in the last. 



256. SPENCER'S PLEUROSIGMA (Pleurosigma Spencerii)* 



3 2 



