10 v. T. OLEVE, SYNOPSIS OF THE NAVICULOm DIATOMS. 



Naviculse Lineolatse Cl. 



Valve elongated, rarely constricted, sigmoid or asymmetrical. Axial area usually indistinct 

 or narrow, rarely wide. Central area small or large. Structure: radiate or parallel strise, finely 

 and transversely lineate, the lineation always closer than the stri?e. Connecting zone not com- 

 plex. — Nav. distans and N. directa have two chromatophore-plates along the connecting zone. 

 Their margins are not indented. N. {Schiisonema) mollis has the same arrangement of the cell- 

 contents. 



This section corresponds to the groups Radiosce, Retusm and Directce of GtKUNOW and com- 

 prises a very large number of forms, frequently nearly connected or passing into each other. 

 Their most characteristic feature is the lineation of the striae. The latter are usually radiate in 

 the middle of the valve and divergent, parallel or convergent at the ends. In several forms the 

 striee are parallel throughout. In those forms in which the median strise are radiate, they are 

 also frequently alternately longer and shorter. 



This group is connected by a few forms {N. Placentula) with the Naviculse Punctatse. As 

 a rale the Lineolatse incline to a lanceolate or linear outline, while the Punctatse are elliptical. 

 The principal distinction between both groups is that the strise of the Punctatse are composed of 

 distinct puncta, usually as widely apart as the strise, but in the Lineolatse the puncta are much 

 closer, the distance between the lineolte being less than the distance betM'een the strise. In some 

 cases (for instance Nav. tusculu) the strise are crossed by longitudinal blank lines and have then 

 very much the appearance of the striation in the section Punctatse. Such forms may in most 

 cases be distinguished from the Punctatee by the terminal strise being parallel or convergent. 



Among the asymmetrical diatoms there is a close relation between the GymbeUce and this 

 section, both having in many cases an exactly similar striation> Several intermediate forms exist. 

 For instance Nav. dicephala is nearly akin to Cymhella anglica, and the frustules of Cymhella 

 Ungeri are frequently so nearly symmetrical, that this species might be classed among the 

 Lineolatse. Among the Amphorae there is one species only, as far as I know, which seems to be 

 closely akin to the Lineolatse (Amphora labuensis). Passages between the perfectly symmetrical 

 and decidedly asymmetrical are offered by Nav. mediterranea and Nav. toxonidea. 



The forms of this group, which have the strise crossed by several longitudinal blank lines, 

 suggest a connection with the genus Trachyneis. 



The species of the group Lsevistriatse are no doubt nearly connected with those of the 

 Lineolatse. They have the same general outline, and the strise are in similar directions, but 

 those of the former are apparently smooth. 



Artificial Jcey. 

 ^ j Median line sigmoid . . . . N. Sigma Bktjn. 



straight ... 2. 



I Axial area distinct or broad 3. 



' \ — — vei'y narrow or indistinct . . . . . 16. 



Axial area bilateral . . . . 4. 



unilateral . . . . N. scalarifer Brun. 



„ I Axial are 



. J Axial area asymmetrical . . N. irregularis Pant. 



' ( -^ — symmetrical ... . . . ,5. 



p. f Valve constricted in the middle . . . . ^, Chi Cl. 



■ I — not — — — .... 6. 



' Besides: N'. irregularis Pant.. N. superba Cl., N. transitans var. incudiformis, var. asymmetrica, N. spuria 

 var. asymmetrica, N. imperfecta Cl., N. monodon Beun, N. Anthracis Bk. and Cl., N. valida Cl. 



