154 SKETCH OF THE INFUSORIA 



SVNEDUA. 



Carapace simple, siliceous, fixed ivhen young hy one extremity, 

 when older often free, longer than broad, foot either wanting or 

 rudimentary, form elongated or prismatic. 



Syncdia ? (PI. Ill, fig. 1) Frustules long, slender, linear, 



adhering laterally into plates whicli are supported by a short fleshy 

 pedicel, and terminated by a fleshy mass. 



The species whose usual appearance is shown in PI. Ill, fig. 1, 

 occurs in vast quantities on various Algae in the Hudson River 

 at West Point. It usually completely envelopes the plants to 

 which it is attached, giving them a covering of bristling crystal- 

 like particles, through which it is often difficult to see any portion 

 of the supporting plant. When the Mgm on which it grows are 

 dried, they often have a greenish gray hue, from the presence of 

 this parasite. 



It presents considerable resemblance to S. Gailloni, Ehr. [Dia- 

 toma crystallinum, Ag.) and has, like that, minute striae on the 

 edges, but I have seen no allusion made in the descriptions of 

 that species to the fleshy projection which is so conspicuous in 

 our species. 



A person who sees how abundant this species is in the recent 

 state, will no longer wonder that, in the lapse of years, masses 

 of infusorial shells should accumulate so as to form extensive 

 strata. 



Sipiedra ? PI. Ill, fig. 2.) Frustules linear, straight, striate, 



truncate on the lateral side, ventral sides with a neck-like contrac- 

 tion near each end, ends rounded. 



This species is very abundant in fresh water near West Point, 

 often covering aquatic plants with a glittering envelope of crystal- 

 like frustules. The individuals are perfectly linear, wdth truncate 

 ends. When seen laterally, they show near their extremities a 

 slight contraction, which forms a neck supporting the round or 

 knob-hke terminations. Minute striae may be seen as represented 

 in the figure. 



This species presents many points of resemblance both to 

 Synedra vlna and Fragillaria rhabdosoma of Ehrenberg, but I 

 cannot identify it positively with either. 



