280 DESCRIPTION OF \^Polygdsiriea. 



otlicr transverse lines that divide the segments themselves into two 

 or more portions. (P. 13, f. 6.) 



" Cloderium may be distinguished from all the other genera of 

 the BesmidiecB by its elongated, curved, entire, and attenuated 

 fronds." 



The discussion as to the vegetable or animal nature of the Closteria, 

 and Ehrenbcrg's views, are given at page 179, and in the inti'oduction 

 to this section of the family Bacillaria. 



1 . — Sporangium orliculor, situated between the conjugating fronds and 

 hut slightly connected with them ; fronds never rostrate fClosteriumJ. 



f Frond semilunate, or semildnceolate, tapering from the middle, the 

 lower margin straight, (or nearly so), and inclined upioards at the end. 



C. lunula (M.) — Large, stout, smooth, semilunate; lower margin 

 nearly straight, inclined upwards at the rounded ends ; vesicles nu- 

 merous, small and scattered. Fillets several ; three more distinct 

 than the rest. Empty frond colourless, without markings, and its 

 suture indistinct. Length l-62nd. 



C. acerosum. — Linear-lanceolate, gradually tapering, ends conical ; 

 fillets distinct ; vesicles in a single series j empty frond colouiiess ; 

 striae none or indistinct (P. 1, f. 63, 64, 65.) 



Yar. fh.J — More elongated; strige more distinct. Length l-170th 

 to l-48th. 



C. lanceolatum. — Semilanceolate, gradually tapering ; ends sub- 

 acute ; fillets several ; vesicles in a single series ; empty frond colour- 

 less. Length l-64th. 



C. turgidum. — Lower margin slightly concave, inclined upwards at 

 the rounded ends ; upper margin with a depression near each ex- 

 tremity ; empty frond coloiu-ed ; striae numerous, fine but distinct. 

 Vesicles in a single row ; fillets three or more ; suture distinct. 

 The curved and rounded ends are characteristic Length l-39th 

 (P. 1. f. 66.) 



■f- f Frond smooth, crescent-shaped, rapidly tapering from the middle- 



C. Ehrenhergii = C lunula (Ehr.) — Smooth, stout, crescent-shaped ; 

 when empty, colourless ; lower margin very concave ; inflated at the 

 middle; ends rounded ; vesicles numerous, scattered. Length 1 -68th. 

 (P. 8. f. 10.) 



C. moniliferum. — Smooth, crescent-shaped, when empty, colourless; 



