156 F. T. CLEVE, SYNOPSIS OF THE NAVICULOID DIATOMS. 



50. N. auklaudica (Irun. (1^63). — V. linear, with broad rounded ends, convex. L. (),o^ 

 to 0,(16; B. 0,0 18 mm. Median line sti'aight, somewhat excentric; its terminal fissures turned in 

 contrary directions and of somewhat unequal length. Axial area indistinct; central very small. 

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

 18 in 0,0 1 mm. Frustule rectangular with rounded corners, somewhat constricted iii the middle. 

 Connecting zone with several longitudinal rows of short strirc (Grun.). — Grun. Verb. 1863 p. 151 

 Pi. V f. 14. Novara p. 17. Icon. n. PI. V f. 15. 



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



A very characteristic species, which seems to be related to N. tumida. 



51. N. Jimboi Pant. (1893). — V. lanceolate, rostrate, obtuse. L. 0,o4l'; B. 0,op.( mm. 

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

 StricE 13 in 0,oi mm. radiate, but parallel at the ends, punctate; puncta about IG in 0,oi mm. — 

 Pant. Ill PI. V f. 81. 



Habitat?: Sentenai' (Pant.). 



This form resembles N. iiiuf/ca, which also has a stigma on the central area, but the central 

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



Cymbella Ag. (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, usually radiate, rows of puncta, 

 or finely lineate striaj 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 l)ranches 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 mass 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 mass of the other mother-cell. 



As early as 1817 Nitszch described some CymbellcE under name the of Bacillaria fulva and 

 B. •phoenicetiteron,, and in 1829 Ehrenberu founded the genus Cocconenta for the stipitate forms. 

 Agardh in 1830 founded the genus Cymbdla (Consp. crit. 1) for diatoms with »frustula 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 Cijmhdla. Later 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 adequately fitting, althougli a 

 little more recent than Cocconema. There can l^e no doubt as to the advisability of uniting Cym- 

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

 differently shaped terminal fissures. On the other hand transitions exist between the downward 

 turned terminal fissures of Encyonema and the reflexed fissures of Cymbella, as for instance in 

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



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

 this characteristic is subject to much variation. Tliere are all transitions from boat-like to almost 



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