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



3. C. circiimvallata Cl. N. Sp. — V. linear-elliptical with broad, rounded, sometimes slightly 

 rostrate ends. L. 0,055 to 0,075; B. 0,oi2 to 0,022 mm. Median line slightly sigmoid, with approxi- 

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

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

 ends, punctate; puncta coarse, forming longitudinal rows, 14 in 0,oi mm. — PL I f. 10, 11. 



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



Diploneis Ehb. (1840). 



Valve usually short, constricted in the middle, or not, generally with obtuse or rounded 

 ends. Central nodule more or less quadrate, prolonged into horns, or processes, which enclose the 

 median line. On both sides of the horns are depressions, or furrotvs, of more or less breadth. 

 Structure: transverse finer strige, or coarser costaj, 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 longitudinal costfe, giving the valve the appearance of being reticulated; or 

 alternate with dotible rows of finer puncta, or alveoli. — The cell-contents (of 

 D. fusca, D. Smithii, D. didyma, D. siibcincta, D. chersonensis and 1>. constricia) 

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

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

 crowded and orbicular small discs. 



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

 navieuloid diatoms. This characteristic is of no importance; but on the other 

 Diploneis Smithii, hand, the central nodule, the furrows and the structure are so peculiar, that the 

 times magnified. t\- ^ ■ \ A A ^^ v A A 



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 Naviculee Lyratse, 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. lyratee, viz. Dipl. Iiyalina Donk. and D. Hudsonis Grun. 

 Outside the horns are depressed parts of the valve, furrows. These furrows have usually a longi- 

 tudinal row of large pearls, formed by the continuation of the costse 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 exterior part of the valve is in several species a space, the lunula, 

 of different structure from the outside part of the valve. Such lunulte occur in D. mirahilis, D. 

 Crabro and others. 



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

 has fine strise, which in JD. Hudsonis are formed by obliquely decussating puncta. In other forms 

 there are coarse costge, not composed of puncta. The costse frequently anastomose and seem then 

 to be crossed by one or more, undulating, or straight, longitudinal ribs. When these longitudinal 

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

 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 costse. A similar structure 

 occurs in Scoliotropis and Gomphoneis. In the larger forms the transverse costse alternate with 

 large rounded pore-like markings, the ocelli, which evidently belong to an interior stratum of the 

 valve. In D. Crabro and allied forms these ocelli form a marginal row, which in the middle ap- 



