348 DIATOMA. 



var. constrictum. (H.V.H. Atl., pi. 51. f. 14, 15*; Type No. 344), 

 plate n, fig. 475, 



Differs from the type form with which it is allied by intermediate forms 

 (see H.V.H. Atl., pi. 51, f. 13), by the superior apex being rostrate 

 capitate. 



Fresh water. Rarer than the type-form. Fays-les-Veneurs (Del.). Ard. Lieg. (De 



Wild.). England (Norman). 



var. Zinkenii. (M. Zinkenii. K'ittz. ; H.V.H. Atl., pi. 51, f. 17*), 

 plate 11, fig. 476. 



Connecting zone showing internal septa. 



Tribe XIV. Diatome.e. 



( Valves without a keel (carina) ..... Diatoma 



( Valves furnished with a carina, the latter not punctate . . Denticula 



GENUS 64. DIATOMA DE CANDOLLE, 1805 



(Char. Emend.). 



Valves lanceolate or linear, furnished with transverse costal, but 

 without a carina ; pseudo-raphe rather indistinct. Frustules with 

 girdle face quadrangular, elongated, united into short filaments or zig- 

 zag chains. Endochrome granular, scattered on the internal surface 

 of the frustules. 



ANALYSIS OF SPECIES. 



f Frustules forming f Valves broadly lanceolate, or linear-elliptic ; apices 



a filament in scarcely or not rostrate or capitate . . D. vulgare. 



zig-zag ; valves j 



with delicate \ 



costse. i Valves narrowly linear, with apices more or less 



(I. Diatoma.) [_ capitate . . . D. elongatum. 



Frustules f 



united in short j Valves lanceolate, with apices sometimes slightly 



filaments ; produced . . . . D. hiemale. 



valves with 



very robust | Valves linear, narrow, with apices rostrate or ros 



costse. j trate capitate ... D. anceps. 



. (II. Odontidium.) [ 



I. DlATOMA. Filaments in zig-zag ; costce rather delicate. 



D. vulgare Bory (Diet, d'hist. natur., 1828, Bot, pi. 20, f. 1; 

 H.V.H. Atl., pi. 50, f. 1-6*; Type No. 335), plate 11, fig. 465. 



