76 P. T. CLEVE, SYNOPSIS OF THE NAVICULOID DIATOMS. 



3. C. circii 111 val lata Cr,. N. Sp. — V. linear-elliptiual with broad, rounded. sometime.s slightly 

 rostrate ends. L. U,o55 to 0,1175; B. 0,ui2 to 0,022 mm. Median line slightly sigmoid. with ajipmxi- 

 mate central pores and prolonged terminal fissures. Axial area narrow; central rhomboidal. 

 Ridges one or two on each side of the median line. Striae 9 in 0,oi mm., parallel, radiate at the 

 ends, piinctate; pnncta coarse, forming longitndinal rows, 14 in 0,oi mm. — Pl. I f. 10, 11. 



Marine: Balearic Islands! Ceylon! Labuan! Japan (Brun Coll.)! 



Diploneis Ehb. (1840). 



Valve usually sliort, constricted in the middle, or not, generally with t)btiise or ronndéd 



ends. Central nodule more or less quadi'ate, prolonged into horits, or processes, which enclose the 



median line. On both sides of the horns are depressions, or furroics. of more or le.ss breadth. 



Structure: transverse iiner strite, or coarser costu?, which usually continue in a 



rudimentary state across the furrows, where they frequently give rise to a longi- 



tudinal row of large pearls. The transverse costse are often crossed by one or 



more longitndinal costre, giving the valve the appearance of being reticulated; or 



alternate with double rows of finer puncta, or alceoli. — The cell-contents (of 



D. fusca, D. Smithii, D. didi/ina, D. aubciiicta, D. cliersonensis and D. coiistricta) 



have two chromatophore-plates along the connecting zone. They are deeply in- 



dented and divided, sometimes in such a manner as to be split np into closely 



crowded and orbicular small discs. 



The name Diploneis was given by Ehrenberg 1840, to some panduriform 



naviculoid diatoms. This characteristic is of no importance; bnt on the other 



Diploneis Snnthn, ];iand, the central nodnle, the furrows and the structure are so peculiar, that the 

 times magnined. t,- i ■ in n.ii 



genus Diploneis may be regarded as a well founded one. 



The central nodule is, in the more typical forms, large and quadrate, with the angles pro- 

 longed into strong siliceous horns, enclosing the median line. In some few forms these horns are 

 less distinct, as in D. nitescens. The horns correspond evidently to the lyre-shaped expansions or 

 lateral areas in the section of Naviculse Lyratte, but in Diploneis the space between the horns 

 and the median line is never punctate as in that group, There are a few forms which are inter- 

 mediate between Diploneis and the Nav. lyratte, viz. Dqil. /ii/alina Donk. and D. Hitdsoiiis Grux. 

 Outside tlie horns are depressed parts of tlie valve, furroics. These furrows have usuallj^ a longi- 

 tudinal row of large pearls, formed by the continnation of the costfe of the valve. Sometimes 

 there are double rows of pearls or alveoli. These furrows are to be found also in other genera, 

 as in Scoliopleura, Cymatoneis, etc, and point to a relationship between Diploneis and those genera. 

 Between the furrows and the exteriör part of the valve is in several species a space, the lumda, 

 of ditFerent structure from the outside part of the valve. Such lunuhe occur in Z>. »rirabilis, I). 

 Crabro and others. 



The structure of Diploneis is very variable. In some forms, as in D. hyalina. the valve 

 has hne striaj, which in B. Hiid.sonis are formed by obliquely decussating puncta. In other forms 

 there are coarse costa>, not composed of puncta. The costiv fre(inentl3' anastomose and seem theii 

 to be crossed by one or more, nndulating, or straight, longitndinal ribs. When these longitndinal 

 ribs are numerous, they form with the transverse costiK a network of quadrate alveoli. The costse 

 often alternate with double rows of puncta (alveoli), forming obliquely decussating rows. These 

 alveoli seem to be formed by numerous small lateral branches from the costa\ A similar structure 

 occurs in Scoliotropis and Gomphoneis. In the larger forms the transverse co.sttE alternate witli 

 large rounded pore-like markings, the oceUi, whicli evident.]}' belong to an interiör stratum of tlu' 

 valve. In I). Crabro and allied forms these ocelli form a marginal row. wliicli in thr niiddlr an- 



