52 



p. T. CLEVE, SYNOPSIS OF THE NAVICULOID DIATOMS. 



Naviculse Lyratse Cl. 



Valve usually elliptical to lanceolate, rarely constricted in the middle. Median line with 

 curved terminal fissures, rarely in contrary direction, or bayonet-shaped. Axial area indistinct. 

 Central area small, united to two, more or less broad, lateral areas. Structure of the valve: 

 usually distinct puncta, disposed in transverse rows, radiate at the ends of the valve, and in 

 undulating longitudinal rows. Zone not complex. 



I have examined some living specimens of N. Lyra, N. spectabilis and N. Hennedyii. All 

 have two chromatoph ore-plates along the valves. The margins of the plates are strongly indented. 

 From the apices a narrow and deep sinus proceeds towards the central nodule and has at its end 

 an elseoplast. As the plates in some cases were deeply constricted in the middle it seems probable 

 that they divide by a fissure at right angle to the median line. 



' — a- 



Nav. Hennedyi with cell-contents, 

 600 times mnguifled. 



Nav. Lyra var. with cell-contents, 

 600 times magnified. 



The most important characteristic of this group consists in the lateral areas, which are to 

 be regarded as lateral expansions of the central nodule. They are more silicious than other parts 

 of the valve, and coherent with the mass of the usually small central nodule. 



This group, corresponding to the Hennedyees and Lyrees in Van Hburck's Synopsis, com- 

 prises an enormous mass of forms, in which are more transitions than in any other group of navi- 

 culoid diatoms. All the characteristics are subject to so much variation, that I am unable 

 to distinguish more than a very few, well defined species, although besides the numerous pu- 

 blished figures I have examined at least 300 sketches of forms from all parts of the world. 



I have tried to obtain characteristics from the relative number of the striae and their 

 puncta, but the variation, even in the same species, is too great. The outline of the valve oifers 

 no trustworthy characteristics, the same species occurring with rounded, obtuse and rostrate 

 ends. The breadth and form of the lateral areas are also subject to great variations, so that all 

 possible transitions can be traced from the large lunate areas of N. Hennedyi to the narrow and 

 linear areas of N. Lyra. The presence or absence of markings in the areas offer no characteristics 

 for specific distinction. Inspection of a large number of specimens has induced me to unite in 

 one species a considerable number of forms, hitherto admitted as distinct species. The forms be- 

 longing to N. approximata, N. Hennedyi, N. spectabilis, N. clavata and N. Lyra are numerous, 

 and the simplest and most effective course would perhaps have been to unite these five species, 

 and possibly others; as they all pass by numerous intermediate forms into each other. 



