124 P. T. CLEVE, SYNOPSIS OF THE NAVICULOIl) DIATOMS. 



This genus includes one species only, which I cannot place in any other group. The thick 

 lines on both sides of the median line seem to point to some relation to Friistulia. 



1. S. inconspiciia Greg. (1857). — V. linear, frequently gibbous in the middle, with broad, 

 roiinded ends. L. 0,o5; B. 0,oo7 mm. Central nodule very small; terminal nodules small, some- 

 what distant from the ends. Median line bordered by two strong, siliceous ribs. Axial area 

 indistinct. Central area a broad, transverse fascia. Strite 26 in 0,ui mm., parallel throughout. 

 — N.? inconspicua Greh. D. of Clyde p. 478 Pl. IX f. 3. N. Fistula A. S. N. S. D. Pl. Il f. 29 

 (1874). Stenon. incomp. Icon. n. Pl. V f. 28. 



Marine: North Sea! Scotland (Greg.), Bohuslän! Balearic Islands! 



Var. Haculus Cl. (1883). — L. 0,065; B. 0,oo7 mm. Strife 19 in 0,oi mm., crossed in the 

 middle by a narrow lateral area. — -A^. Baculus Cl. Vega p. 474 Pl. XXXVII f. 51. 



Marine: North Siberian Sea, Cape Wankarema! 



Cistula Cl. N. g. 



Valve broad (of the only known species, rectangular). Central nodule very small. Median 

 line between two siliceous ribs; its central pores very approximate. Structure: slightly radiate 

 strise, crossed by several longitudinal, blank bands. 



This group contains but one species, which 1 am unable to place in any other. The peculiar 

 form of the median line is nearly the same as in Stenoneis and Frustulia. 



1. C. Lorenziana Grdn. (1860). — V. rectangular, sometimes slightly gibbcus in the middle 

 and at the ends. Strife slightly radiate throughout, 17 in 0,oi mm., composed of elongated puncta, 

 arranged in regular longitudinal rows, 12 in 0,oi mm., angularly bent in the middle. — Nav. Lo- 

 renziana Grun. Verh. 1860 p. 547 Pl. III f. 3. Nav.? Cistella Grev. T. M. S. XI p. 19 Pl. I 

 fig. 12 to 14 (1863). Cistula Lor. Icon. n. Pl. I f. 31. 



Marine: South coast of England (Roper), Balearic Islands! Adriatic! Queensland (Grev.)' 

 Port Jackson! Campeachy Bay! 



Brebissonia Grun! (1860). 



Valve symmetrical, lanceolate or subrhomboid. Central nodule elongated. Terminal fissures 

 almost straight. No longitudinal lines. Structure: coarse, transverse, costate striiE and very fine 

 puncta arranged in very fine longitudinal strife. Connecting zone simple. Cell-contents: a single 

 chromatophore-plate as in Cymbella. 



The only species of this genus was in 1838 described by Ehrenberg as Cocconema Bocckii. 

 It was in 1853 placed by W. Smith in the genus Dory^jhora together with Rhajjhoneis amphiceros. 

 Grunow in 1860 formed for this species the genus Brehissonia (Verh. 1860 p. 512), principallj- 

 characterized by the occurence of the symmetrical frustules on gelatinous stalks. Heibercj in 1863 

 placed it in Navicula, a genus to which it has scarcely any affinity, and from which, according to 

 the researches of Pfitzer (Bau u. Entw. p. 76) it differs greatly in its cell-contents, which are 

 similar to those of Cymbella. There is no doubt good reason for placing it in the separate genus 

 Brebissonia. By its elongated central nodule it seems to approach to Amphiplenra, but the 

 structure of the valve is different, and is more like that of the group Lineolatce in the Naviculm. 

 It is at any råte an isolated form of doubtful place in the system. The only known species occurs 

 in brackish water attached by gelatinous stalks to water-plants. 



