DesmidiecB.'l infttsorial animalcules. 243 



Var. (b.) — Filaments plane ; crenaturcs shallower and sliglitly 

 angular. (P. 2. f. 108.) 



ApTOGONim Baileyi. — Filament not crenated ; joints about equal 

 in length and breadth. Filament triangidar ; angles, in end view, 

 rounded. 



Genus Sph^eeozosma (Corda.) — Filament plane, fragile; joints 

 closely united by means of glandular processes, and deeply divided on 

 each side, thus forming two segments, and giving a pinnatilid 

 appearance to the filament. Filaments pale green, gelatinous, pro- 

 bably not twisted. Transverse view linear or oblong. This genus 

 differs from Besmidium, Bidymoprium, and Hyalotheca, in its flat 

 filaments (not t^dsted), in the deep division of the joints into seg- 

 ments, and especially in the presence of the minute gland-like 

 processes at the junction of the joints. On account of its deeply 

 constricted joints, this genus forms a connecting link between the 

 preceding and the following genera. 



S. vertehratum = ( Odotdella (?) unindentata, Ehr.) — Joints as broad 

 as long, deeply divided into two segments by a narrow notch on each 

 side ; junction glands oblique, soHtary at the centre of each margin. 

 It is furnished with a broad, colourless, and veiy delicate mucous 

 Bheath. (P. 2. f. 107.) Length l-1429th. 



S. excavatum. — Joints longer than broad, having a deep sinus on 

 each side, and two sessile glands on each margin at their jimction. 

 Filament minute, fragile. The sporangium is formed between the 

 conjugating joints, and is elliptical in figure. 



S. lamelliferum (Corda.) — Filaments short; nearly uniform; joints 

 divided by a transverse line to one-third of their depth, segments 

 rounded. 



^.pulchrum (Bailey.) — Joints twice as broad as long, deeply incised 

 on each side ; junction-margins sti'aight, connected by short bands. 

 It is twdce as large as S. vertehratum. 



^.filiforme = OdonteUa {}) JiUformis and Tessarthra filiformis (Ehr.) 

 — Joints bilobed, xmited by double slender processes, which enclose 

 a quadrate foramen between each pair. 



S. serratiim (Bailey.) — Joints broader than long, deeply notched or 

 divided into two transverse portions, with acute projecting ends, 



