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



(i. D. niastogloidea Pant. (1886). — V. strongly constricted, with cnneate, obtuse enis. 

 L, 0,078; B. 0,024; at tlie constirction 0, 013 mra. Marginal cellules about 10 in 0, 01 mm. Cellules 

 of tlie valve 14 in 0,oi mm. — Nav. mast. Pant. I. p. 27 Pl. XXI f. 192. 



Marine: Hungary, fossil (Pant.). 



This species appears, to jiidge from the fig. in Pantocsek's work, to connect 7). marginaia 

 and D. jamaicensis 



I 



7. D. riigosa Temp. a. Brun. (1889). — V. narrow, about 7 times longer than broad. gently 

 constricted, and witli linear, siibtruncate segments. L. 0,2 to 0,22.5; B. 0, 026 to 0, 03. at the con- 

 striction 0,oi3 mm. Terminal fissures in contrary directions. Marginal cellules small, 5 in 0, 01 

 mm. Cellules of the valve obscure. — Mastogloia rugosa Temp. a. Brun. D. foss. du Japon p. 39 

 Pl. IX f. 20. Dicttjoneis rugosa Cl. Diatomiste I. p. 17. A. S. Atl. CLX f. 33. 



Mariue: Japan, fossil (Temp. Br.). 



8. D. Pantocsekii Cl. (1890). — V. gently constricted, with tongue-shaped segments and 

 obtuse extremities. L. 0,ii; B. 0,034, at the constriction 0,027 mm. Median line with the termi- 

 nal fissures in contrary directions and approximate central pores. Marginal cellules 5 in 0, 01 mm., 

 of equal size, forming an uninterupted marginal band. Cellules of the valve about 17 in 0, 01 mm., 

 arranged in irregularly undulating transverse and longitudinal rows. Transverse strise 25 in 0, 01 

 mm. — Navic. niastogloidea Pant. II Pl. XXVI f. 387. — Diet. Pant. Cl. Diatomiste I p. 16. 



Marine: Himgary, fossil! 



9. D. panduriforniis Cl. (1881). — V. slightly constricted, with tongue-shaped segments 

 and obtuse ends. L. 0,097; B. 0,027, at the constriction O.019 mm. Terminal fissures in contrarj' 

 directions. Marginal cellules about 4 in 0, 01 ram., af unequal size, absent in the middle and at 

 the ends. Transverse stria; 20 to 21 in 0,oi mm. — Mastogloia pandiiriformis Cl. X. R. D. p. I 

 Pl. I f. 1. Diet. pand. Cl. Diatomiste I p. 16; 1890. 



Marine: Galapagos Islands! 



Pleurosigma W. Sm. (1852). 



Valve linear to lanceolate, more or less sigmoid, symmetrical. Median line sigmoid with 

 small central nodule and the ends turned in contrary directions. Axial area iudistinct. Central 

 area indistinct or small. Structure: small puncta disposed in transverse and oblique rows. Xo lon- 

 gitudinal lines. Frustule with narrow, simple zone, a:'cuate or not. — Cell-contents (of P. angula- 

 tum) two chromatophores, indented at their margins. The median part of each chromatophore 

 branches into a large elongated lobe along the interiör of one of the valves, and into two similar 

 lobes on the other valve. Division begins by a fissure across the median lobe. After the division 

 of the cell the parts of the chromatophore migrate to the inner side of the old valves (O. Muller, 

 Ber. d. Deutsch. Bot. Ges. 1883 p. 478). 



The sigmoid Naviculaä were named Naricida Sigma by Ehrenberö. Hassall (A. Historv of 

 Brit. Freshw. Algaj 1845 p. 435) proposed for them the name Giirosigma, which was adopted by 

 Rabenhorst (Die Stissw. Diat. 1853) but not by other diatomists, who preferred the newer name 

 Pleurosigma formed 1852 by W. Smith, who published the first monograph of tlie species ("Ann. 

 Mag. Xat. Hist. 2 ser. IX p. 1). The genus Pleurosigma, as aecepted by all diatomiste, includes 

 forms with a structure of small puncta or alveoli, disposed in transverse rows, which are crossed 

 by other rows, either longitudinal, or obliquelj' decussating. There are no intermediate forms be. 

 tween tliese two types, and I think they may justly be regarded as ditferent genera. For the 

 forms with the puncta in transverse and longitudinal rows, I adopt the name Gyrosigma, although, 



