482 DEscEiPTioN OF [Poli/ffastrica. 



Syjstedea vitrea. — Large, linear ; laterally, dilated at each end ; dor- 

 sally, suddenly attenuated at the ends, which are slender hut obtuse. 



Q. praemorsa. — Large, widely linear; laterally, with cuneate, 

 truncate ends ; dorsaUy, with wedge shaped, rounded ends. 



S. Danica. — Large, weak; laterally with the ends dilated and 

 truncate ; dorsally taj)ering on each side from the centre towards the 

 apex, which is dilated, roimd and obtuse. Length 1- 140th. 



S. splendens. — Very large, elongate ; laterally dilated at each end, 

 which is truncate ; dorsally tapering from, the centre gradually to 

 each of the rather obtuse ends. Length l-72nd. 



S. Biceps. — Large, dorsally curved near the ends, and constricted 

 so as to form a rounded head. Length 1- 100th to l-60th. 



S. Armoricana. — Large, turgid; laterally widely linear, sigmoid, 

 truncate, the margin having glandlike (dotted) striae ; dorsally, nar- 

 rowly linear, straight, apices attenuate and rather obtuse. Length 

 1-1 08th. 



S. sigmoidea. — (Kiitz) = Navicula sigmoidea. Ehr. 



S. vermicularis. — Small, slender, linear, truncate, sigmoid and 

 smooth. Length 1 -200th. 



S. sigma. — Kather small, sigmoid, each end slightly attenuate, 

 truncate margin delicately striated. Length 1-1 40th. 



S. parvula. — Small, narrowly linear, smooth ; laterally truncate at 

 the apices, dorsaUy narrowly lanceolate. Length 1 -960th. 



S. Acus. — Smooth, slender, of moderate size ; laterally, rather at- 

 tenuate towards the truncate ends ; dorsally, very narrowly lanceolate 

 or acicular. Length 1 -260th. Hamburgh. 



S. familiaris. — Rather small, smooth, very distinctly tabulate and 

 broken up in a liabeUate (whiplike) manner, laterally rather tapering 

 towards the truncate ends ; dorsally lanceolate, acute. Length 

 1 -320th. 



S. pulchella = Exilaria pulchella (Ralfs) — Eather small, tabular, 

 expanding in a flabellate manner from the point of attachment ; 

 laterally smooth, attenuate towards each end, which is truncate ; 

 dorsally naiTowly lanceolate. Length 1 -360th. 



S. Mucicola. — Imbedded in mucus, wands smooth ; a few conjoined 

 in a flabellate manner ; somewhat attenuate towards each end, ends 

 truncate. Length l-650th. 



