452 DESCRIPTION OF IPali/'^atilrica. 



and particularly in its pedicle being of less length than the individuals 

 it supports (figs. 199, 200, 201.) The clusters are sometimes many- 

 inches in length, (fig. 202 a more magnified specimen.) Length 

 l-860th. to l-180th. In saltwater. 



AcHNAiJ^THES suhsessUts. — Rather small, slender, striated,' sUghtly 

 bent, rectangular ; individuals single or binate ; end view oblong or 

 elliptic, with rounded apices; stipes thick, very short, or almost 

 wanting (obsolete.) Length 1-11 50th. to 1 -430th. Var. I. multiarti- 

 culata; in which more than two individuals are conjoined in a band. 

 Common in fresh and salt water. 



A. Exilis. — Small, slender, quite smooth, rectangular; end view 

 lanceolate, acuminate ; pedicle slender, often longer than the body. 

 Length l-1150th. to l-570th. On Confervse in freshwater; not 

 common. Dark reddish brown when recent. 



'' The Achnanthes exilis (Ralfs) agrees with Kiitzing's specimen 

 in its crowded habit and elongated stipes, but its frustules are much 

 smaller, and its lateral surfaces less acute, in both which respects it 

 is intermediate between A. minutissima and A. exilis, (Kiitz.)" 



A. minutissima. — Very small, slender, and smooth ; end view lan- 

 ceolate ; stipes fine, short, or about the length of an individual. 

 Length l-1200th. to l-800th. Common on fresh water Algae and 

 Confervse. This and A. exilis diff'er from the other species by their 

 fresh- water habit ; from A. exilis it differs by its short stipes, and its 

 less acute lateral surfaces. 



A. inequalis. — Unequally bent, and smooth. Fossil in Sweden. 



A. pachypus. — Small, finely striated, slightly curved at the centre 

 of ventral surface ; dorsum rather turgid, apices rounded, angles 

 obtuse ; end view lanceolate-elliptic ; pedicles very short and thick. 

 Length 1-1 730th. to 1-1 320th. Brackish water, Peru. Young 

 specimens of A. subsessilis are very similar to the present species, 

 which has seldom more than thi'ee joints, never more than four ; 

 Dr. Montague, its first describer, gives only two. 



A. rhomhoides. — Frustules veiy turgid, ventral surface with acute 



extremities, and rhomboid-lanceolate ; stalk distinct, short and thick. 



A. turgens. — Viewed laterally (in front view, Ralfs) the 



lorica is three times longer than broad; ventrally, oblong -lanceolate. 



