Naviculacea.'} infusoeial animalcules. 349 



at each end, cormected in a chain by a short fililbrm isthmus ; strioc 

 seven in l-1200th. Freshwater. Length l-288th. This species is 

 described by Mr. Ealfs, thus, — " Frustules plane, several times longer 

 than broad; fi'ont suii'ace with the ends dilated." 



DiATOMA. Ehrenhergiu = Bacillaria elongata (Ehr.) — Attached, 

 stalk minute ; segments strong, rather contracted at the centre ; 

 laterally dilated at the middle, and contracted near the capitate 

 ends; concatenated by a distinct isthmus. Length 1 -456th. 

 Germany. (P. 3, f. 169.) 



D. stellaris (Bailey.) — Frustules rectangular, many (eight) times 

 longer than broad, usually in groups of five or six individuals, 

 cohering by the adjacent (not alternate) angles, so as to produce 

 stellate groups of minute frustules. Common from Rhode Island 

 to Florida. 



Genus Dicladia. — Lorica bivalve, not concatenated ; imilocular ; 

 valves unequal, one simple and tui'gid, the other two horned ; the 

 comua sometimes branching. 



In form this genus approaches Rhizoselenia. In respect to its 

 position in the family Bacillaria, Ehrenberg appends a note of 

 interrogation. 



D. Capreohis. — Smooth, bifurcc^ at one end. Diameter 1 -960th. 

 Virginia. 



D. (?) chtJirata. — Smooth, with intersecting lines, (latticed); 

 remarkable by its rounded outline, and two unequal frontal horns. 

 Diameter 1 -960th. Vii'ginia. 



D. attenuata. — Smooth, with two simple horns at one end, with 

 some parallel, long, acute, and jointed corniculi (setae) about then- 

 base, resembling antennce : the other end unknown. Antarctic Sea. 



D. bulbosa. — One end with two simple horns, with corniculi diverging 

 at the base, but converging at the apex ; bulbous in the central part 

 and rather sulcate (furrowed) ; the other end unknown. Diameter 

 of a fi-agment of the one valve l-782nd. Antai-ctic Ocean. 



Genus Dicxyolampka (Ehr.) — Bivalve ; orbicular, not concatenate ; 

 disc not perforated ; internal septa absent ; valves equal, cellular 

 only at the centre, their margin radiated, but otherwise smooth. 



From these chai'acters this genus would seem to be closely allied 

 to Codciiiodisciis and Orusjjcdodiscus ; to differ from the former by the 



