180 p. T. CLEVE, SYNOPSIS OF THE NAVICULOID DIATOMS. 



Var. alpestris Be. (1880). — L. 0,027 to 0,033; B. 0,oi2 to 0,oi5 mm. V. truncate, with 

 strongly sigmoid axial area, dilated in the middle to a large subquadrate central area. Strife 

 about 2;-) in 0,oi mm. Lower V. with small central area, strige about 25 in 0,oi man. — Ach. flex. 

 B. D. des Alpes PI. Ill f. 26. Diatomiste II p. 72 PI. V f. 15. 



Alpine regions: Switzerland! Norway (Br.), Auvergne (Br.). 



DlSGoneis Cl. N. G. 



Valves in outline elliptical, without marginal rim, very dissimilar. Upper valve coarsely 

 costate, with narrow axial area. Lower valve without axial area, and with punctate radiate strise. 



The forms placed in this genus are not closely connected. As to their affinities it may be 

 noted that the lower valve of C. Lyra perfectly resembles a small form of Navicula Hennedyi, 

 and that of C. reticulata a small form of the section Punctatce of Navicula. The lower valve of 

 C. pinnata has a great resemblance to C. Pediculus or G. pseudomarginata, and G. formosa in its 

 lower valve recalls C. costata. 



Costse of the upper valve anastomosing into a reticulnm 2. 



— — not — — — — 3. 



area narrow, lanceolate . . C. formosa Brun. 



Artificial key. 

 . I Costse of t 



j Axial are 



■ I — — a silicious rib C. reticulata Cl. 



„ I Axial area of the upper valve very narrow . 4. 



' I — — — — — lanceolate . . .... 5. 



Gestae alternating with double rows of coarse puncta G. Lyra A. S. 



— crossed by fine oblique striae , C. hexagona Be. Cl. 



Gestae alternating with rows of short lines C. versicolor Bb. 



— — — double rows of fine puncta . . . C. pinnata Geeg. 





1. A. hexagona Br. a. Cl. (1891). — Outline broadly linear, with cuneate ends. L. 0,042; 

 B. 0,02 mm. Upper V. with very narrow axial area. Strige 11 in 0,oi mm., parallel in the 

 middle, radiate at the ends, crossed by a set of close oblique strige, about 25 in 0,oi mm. Lower 

 V. with very narrow axial area. Median line straight; central nodule transversely dilated to a 

 stauros not reaching the margin. Strige 13 in 0,oi mm., transversely lineate, strongest near the 

 margin, faint on other parts of the valve. — D. especes nouv. p. 5 PL XIX f. 3 a, b. 



Marine: "Western Africa and Nossibe (Brun.), Yokohama (Brun Coll.)! 



The lower valve has some resemblance to C. costata, but the upper differs in its structure, 

 and especially in the absence of the marginal ring. 



2. C. Lyra A. S. (18-74). — Outline elliptical. L. 0,023 to 0,o6; B. 0,oi4 to 0,033 mm. 

 Upper V. without area, but with an axial rib sending off on both sides parallel (at the ends 

 radiate) costse (about 7 in 0,oi mm.) alternating with double rows of puncta, about 15 in 0,oi 

 mm., forming longitudinal rows. Lower V. with straight median line, and transverse central area, 

 united on both sides to a broad linear area, so as to form a lyre-shaped figure. Strige 15 in 0,oi 

 mm. not distinctly punctate. — N. S. D. p. 93 PL III f. 19 (right figure, lower valve). G.? 1. c. 

 f. 18 (upper figure, upper valve). C. norvegica Grun. Cl. M. D. N:o 102 (1878) upper valve. 



Marine: Grip and Bergen, Norway! 



This curious and isolated form has exceedingly different valves, which I have found to- 

 gether in the same frustule. The lower valve resembles a small form of Navicula Hennedyi. 



3. C. reticulata Cl. N. Sp. — Outline elliptical. L. 0,03 to 0,035; B. 0,oi7 to 0,o2 mm. 

 Upper valve with an axial rib sending off, laterally, transverse costge (about 6 in O.oi mm.) ana- 



