DICTYONEIS. 



157 



Sifl ': 



1 I 



gag 2;f: 



I 



be re-united with Mastogloia or made a special section of it, which would have 

 for its characteristic the binary number of the loculi and their isolation 

 at the median part of the valve where they are found. In true Mastogloia 

 the loculi always form a long marginal line, either straight or curved. 



GENUS 5. DICTYONEIS CLEVE, 1890. 



Valve elongated, of variable form, contracted or not at the median 

 part. Raphe straight, surrounded by a very narrow 

 hyaline zone, with apices generally in opposite directions. 

 Valve with two layers superposed ; the external with fine 

 puncta arranged in quinqunx, the interior with cells 

 broader, vesiculate, giving a reticulate appearance to the 

 stratum. Marginal cells often much broader than the 

 others and simulating loculi. 



The genus Dictyoneis includes eight species which had been 

 ranked by others in the genera Navicida, Pseudo-diploneis and 

 Mastogloia. 



None ot these species belong to the North Sea. 



The form represented opposite belongs to D. marginata CI. 



The forms united under the genus Dictyoneis have a different 

 structure to all other raphidiese ; this structure being in reality 



Dictyoneis 



marginataCl. similar to that observed in many Coscinodiscus and Triceratium. 



" The large marginal cells have the appearance of the loculi of the genus 

 Mastogloia which have caused many of the species to be placed in the latter 

 genus. However 1 find that these cells or loculi belong to the valve itself and 

 not to a separate stratum as in the Mastogloia " (Cleve). 



Fig 



29. 



