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



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

 strongly sigmoid axial area, dilated in tlie middle to a large snbqnadrate central area. Strife 

 about 23 in 0, 01 mm. Lower V. with small central area, striee aboiit 25 in 0, 01 mm. — Ach. flex. 

 B. D. des Alpes Pl. III f. 26. Diatomiste II p. 72 Pl. V f. 15. 



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



Disconeis Cl. N. G. 



Valves in outline elliptical, witbout marginal rim, very dissimilar. Upper valve coarsely 

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



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. Pedicuhis or C. pseudomarginata, and C. formosa in its 

 lower valve recalls C. costata. 



'I 

 'i 



'! 



Ärtificiccl Itey. 

 Costae of the upper valve anastomosing into a reticuluni 2. 



Axial area narrow, lanceolate C. formosa Brun. 



— — a silicions rib G. reticulata Cl. 



Axial area of the upper valve very nai-row 4. 



— — — — — lanceolate 5. 



Costa alternating with double rows of coarse punota C. Lyra A. S. 



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



CostK alternating with rows of short lines C. versicolor Br. 



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



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

 B. 0,02 mm. Upj^er V. with very narrow axial area. Striae 11 in 0, 01 mm., parallel in the 

 middle, radiate at the ends, crossed by a set of close oblique striaj, about 25 in 0, 01 mm. Lower 

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

 stauros not reacliing the margin. Strite 13 in 0, 01 mm., transversely lineate, strongest near the 

 margin, faint on other parts of the valve. — D. espéces noiiv. p. 5 Pl. XIX f. o «, h. 



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



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

 and especially in the absence of the marginal ring. 



2. C. Lyra A. S. (1874). — Outline elliptical. L. 0,023 to 0,og; B. 0,oi4 to 0,033 mm. 

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

 radiate) costse (about 7 in 0,01 mm.) alternating with double rows of puncta, about 15 in 0,oi 

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

 united on botli side.s to a broad linear area, so as to form a lyre-shaped lignre. Striie 15 in 0,ui 

 iiini. not distinctly punctate. — N. S. D. p. 93 Pl. Ill f. 19 (right fignre, lower valve). C? 1. c. 

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



Jhirine: Grip and Bergen, Norwaj'! 



This curious and isolated form lias exceedingly different valves, which 1 have found to- 

 gcilifr in the sainf frnstnlc Tlic lower \-ah'e resembles a snuill form of Navirnla Iloiiinlyi. 



;;. ('. reticulata Cl. N. Sp. — Outline elliptical. L. n,i):i to 0,(I3.'j; B. 0,oi7 to 0,02 mm. 

 Upper Viihi; witli an axial rilj seiuling oif, laterally. transvcr.se costa'. (about (1 in O.oi mm.) ana- 



