156 P. T. CLEVK, SYNOPSIS OF THE NAVJCULdlO IJIATOMS. 



50. N. aiiklandica Grux. (1863). — V. liiiear, with broad roiimled ends, coiivex. L. ö.o.t 

 to 0,06; B. 0,018 mm. Median line straight, nomewliat exceiitric; its terminal tissures turned in 

 contrary directions and of some\vhat niiequal leiigth. Axial area indistinct; central ver}' small. 

 StricB 10 (middle) to 14 (ends) in 0,oi mm., slightly radiate throughout, punctate, puncta about 

 18 in 0,01 mm. Frnstule rectangular with rounded corners, somewbat constricted in tlie middle. 

 Connecting zone with several longitudinal rows of short striis (C-rrun.). — Grux. Verb. 1863 p. 151 

 Pl. V f. 14. Novara p. 17. Icon. n. Pl. V f. 15. 



Marine: Aucklaiul (Grun.), Port Jackson! Australia! 



A very cbaracteristic species, wbicb seems to be related to N. fumkla. 



51. N. Jimboi Pant. (1893). — V. lanceolate, rostrate, obtnse. L. 0,042; B. 0,oi9 mm. 

 Axial area iiulistinct. Central area small, transverse, with a stigma, close to the central nodule. 

 StricE 13 in 0, 01 mm. radiate, but parallel at the ends, punctate; puncta about 16 in (),ui mm. — 

 Pant. III Pl. V f. 81. 



Habitat?: Sentenai* (Pant.). 



This form resembles JSf. iituHca, which also bas a stigma on the central area. but the central 

 area of N. Jimboi is very small. It is doubtful whether it should be jilaced in this group. 



Cymbella Au. (1830). 



Valve elongated, boat-shaped or more or less asymmetrical to the longitudinal axis. Median 

 line excentric. The terminal nodules near the ends of the valve, and the terminal fissures turned 

 to the dorsal, or ventral, side, or straight. Structure transverse, usualh' radiate, rows of puncta, 

 or iinely lineate strite on both sides of the median line. Connecting zone not complex. Cell- 

 contents a single chromatophore, the longitudinal axis of which follows the dorsal part of the con- 

 necting zone. The chromatophore covers the inside of the frustule, with the exception of the 

 ventral part of the connecting zone and the branches of the median line. The division of the 

 chromatophore begins in the ends of the plate on the dorsal side. In conjugating, the mother- 

 cells, usually produced by division of a parent cell, and enclosed in a gelatinous mäss produce two 

 auxospores, parallel to the mother-cells. Before conjugation the cell-contents of one of the mother- 

 cells is divided into two masses, each of which unites with a similar mäss of the other mother-cell. 



As early as 1817 Nitszch described some Cymbellpe under name the of BaciUaria fulva and 



B. phoeniccnteron, and in 1829 Ehrenberg founded the genus Cocconema for the stipitate forms. 

 Agardh in 1830 founded the genus Cymbella (Consp. crit. 1) for diatoms with sfrustula elliptica, 

 libera vel muco amorpha involuta, binatim conjuncta). Some of the species included by Agardh 

 in this genus belong doubtless to what we now name Cymbella. Låter on, in 1830, Kutzing 

 created the genus Encyonema for the cymbelloid forms included in gelatinous tubes. Most authors 

 since then have adopted these three genera and have regarded as Cymbella, forms which live free; 

 as Cocconema, forms attached to gelatinous stalks; and as Encyonema, forms included in tubes. 

 The valves of all these forms are in all essential points similar, and frustules of stipitate or enclosed 

 forms frequently occur free; for which reasons Heiberg (Consp. Crit. Diat. p. 107) 1863 united them 

 in one genus, for which he considered the name Cymbella more adequatelj' titting, although a 

 little more recent than Cocconema. There can be no doubt as to the advisability of unitiug Cvm- 

 bella and Cocconema, but some hesitation may be felt in uniting Encyonema which has somewhat 

 difterently shaped terminal fissures. On the other hand transitions exist betweeu the downward 

 turned terminal fissures of Encyonema and the retiexed fissures of Cymbella, as for instauce in 



C. hclcctica; and I think it most convenient to follow the proposition of Heiberg. 



The most cbaracteristic feature of Cymbella is the asymmetrical form of the valves, but 

 this cbaracteristic is subject to much variation. There are all transitions from boat-like to almost 



