for the Microscope. 29 



201. FOUR-RIBBED EUNOTIA (Eunotia tetraodoii). In 

 this genus the valves are also bent, as in the last, but 

 there are little nodules at the extremities, there are no 

 ribs, and the delicate strice are convergent. The present 

 species has four dorsal ridges, which in a side view resemble 

 large blunt teeth, on the outer margin. Boggy pools. (PI. 

 III., fig. 27.) 



202. BROAD HIMANTIDIUM (Himantuhum hdens). 

 The curved valves in this genus bear great resemblance 

 to those of the last, but in the present the frustules are at 

 first united together into a filament, and the striae on the 

 valves are parallel. In this species the valves are pro- 

 portionately broader than in the next, and there is a 

 depression in the centre of the convex side, and one near 

 each extremity. In marshes. (PI. III., fig. 28.) 



203. NARROW HIMANTIDIUM (Himantidium pcctinale). 

 Valves narrower than the last, tapering, but not con- 

 stricted, towards the extremities. More usually united 

 into a filament. 



204. COMMON MERIDION (Meridian dnulare). The 

 frustules in this genus are wedge-shaped, and united to- 

 gether into a spiral filament. The valves in the present 

 species are long, wedge-shaped, rounded at the larger end, 

 and the striae are indistinct. Attached to the stems of 

 water-plants in clear streams. (PI. III., fig. 29.) 



205. BLUNT ODONTIDIUM (Odontidium mutabile). In 

 this genus the frustules are quadrangular, and united in a 

 filament. The valves are either elliptical or cross-shaped, 

 with conspicuous ribs. This species has oval or elliptical 

 valves, with ribs at the margin. Common in ditches. (PI. 

 Ill, fig. 30.) 



206. POINTED ODONTIDIUM (Odontidium Tabellarid). 

 The frustules do not adhere together so tenaciously as in 

 the last species, and the valves are usually oval, with 

 pointed ends. Common in ditches. 



207. BROAD ODONTIDIUM (Odontidium mcsodoii). Dis- 

 tinguished from the other two species by the broader 

 frustules, and more oval form of the valves, with only 

 from two to four ribs. Common in ditches. 



