10 r. T. CLEVE, SYNOPSIS OF, THE NAVlCrLolD DIATOMS. 



Naviculse Lineolatse Cl. 



Valve elongated, I'arely constricted, sigmoid or asymmetrical. Axial area usually indistinct 

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

 and transversely lineate, the lineation ahvays closer than the striie. Connecting zone not com- 

 plex. — Nar. (lisfans and X. (lircria have two chroniatophore-plates along the connecting zone. 

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

 contents. 



This section corresponds to the groups Radiosce, Rctuscr and Diredee of Grunow and com- 

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

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

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

 striiiB are parallel throiighout. In those forms in which the median stria? are radiate, they are 

 also frequently alternately longer and shoi'ter. 



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

 a rule the Lineolatee incline to a lanceolate or linear outline, while the Punctata are elliptical. 

 The principal distinction between both groups is that the stria; of the Punctata; are composed of 

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

 closer, the distance between the lineolte being less than the distance between the striaj. In some 

 cases (for instance Nar. tnsculu) the stria; are crossed by longitudinal blank lines and have then 

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

 cases be distinguished from the Punctata' by the terminal strife being parallel or convergent. 



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

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

 For instance Nav. dicephala is nearly akin to (Jymbclla anglica, and the frustules of CymhcUd 

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

 Lineolata;. Among the Amphorce there is one species only, as far as I know, which seems to be 

 closely akin to the Lineolatic {Amphora lahuensis). Passages between the perfectly symmetrical 

 and decidedly asymmetrical are offered by Nav. mediterranca and Nav. to.ronidcn. 



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

 suggest a connection with the genus Trachyneis. 



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

 Linecdata'. They have the same general outline, and the stria- are in similar directions, but 

 those of the former are apparently smooth. 



Artificial key. 



J Minliaii line sigmuid i\^ Sigma Britn. 



■ 1 — — straiglit 2. 



^ J Axial area distinct or i)road 3. 



' \ — — very narrow or indistinct 1'5. 



., I Axial area bilateral 4. 



'^' I ^ — unilateral N. sc(dnrifer Brun. ' 



I Axial area asymmetrical N. irrrgidaris Pant. 



\ — — symmetrical •>. 



Valve constricted in the middle N. Chi Ol. 



i). 



{ 



not — — ~- G. 



' Besides: K. irregidarifi Pant.. ' i\\ Huperhn V.h., K. fravfiitaris rar. ivcudifoniils, rar. asyminefrica, N. sptiria 

 var. a.synivicfricd, N. iiii]}crfccfi( Cl., A^. nioiiodov Brun, A'. AiitlirnciH Br. and V\... N. ralida Vl. 



