348 BESCEiPTioN OF [Poli/ffosirtca. 



DiATOMA j'^ff^/wrt!?^. — Segments laterally acutely lanceolate, accord- 

 ing to Kiitzing it = Bacillaria seriata, B. Ftolomoei, and B. jlocculosa 

 (Ehr.) Length l-720tli. 



D. vitreum. — Filaments attached by a very delicate stalk, and 

 made up of few segments ; segments miuute, oblong, glass-like ; 

 ■ftath a longitudinal row of punctiform spaces. It is very closely 

 allied to D. ininimum, Ralfs. Length 1 -1320th. On Algae in the 

 Acb'iatic. 



D. hyalmum. — Segments larger, elongated, very slightly attenuate 

 at each end ; peculiarly hyaline ; lateral aspect lanceolate, rather 

 obtuse; with golden yellow interspaces. Length l-336th. Adriatic. 



Sect. II. Forms striated. 



D. mdgare. — Filaments long, attached by an almost invisible 

 stalk ; segments rectangular, convex, striatedo n the margin ; punctate 

 at each end ; three to four times longer than broad. It = Ba- 

 cillaria jlocculosa and B. vulgaris (Ehr.) (P. 3, f. 168.) Length 

 1 -420th. Pools and streams. Common. 



D. mesodon. — Segments oblong, with a few central dentations, 

 laterally ventricose, lanceolate, with three to four transverse striae 

 at the middle. 



Var. {h.) — Segments quadralS*!^ 



Var. {c.) cuneatum. — Segments cuneiform. It = Bacillaria cuneata 

 (Ehr.) (P. 3, f. 170.) 



D. tenue. — Attached, stalk very indistinct; joints laterally 

 lanceolate, with transverse strisD ; twelve in l-1200th. The form 

 and size of the segments vary. 



Var. {a.) moniliforme. — Joints quadrate. 



Var. {b.) infer medium. — Diameter of joints twice the length. 



Var. (c.) cuneatum. — Segments cuneate. 



Var. {d.) normale. — Joints elongate, slender. 



Var. {e.) — Segments obliquely united. = Bacilla/ria pectinalis (Ehr.) 

 Length 1 -660th. 



D. mesoleptum. — Attached, stalk obsolete ; segments rather con- 

 tracted at the centre, laterally lanceolate ; transverse striae ten to 

 eleven in l-1200th. Length l-650th. Freshwater. 



D. elongatum: — Attached, stalk obsolete ; segments very slender, 

 rather narrower at the middle ; laterally linear, tumid, and capitate 



