76 V. T. CLEVE, SYNOPSIS OF THE NAVK^ULOII) DIATOMS. 



;-5. €. circuiuvaliata Cl. N. 8p. — V. linear-elliptical with broad, rounded, sometimes slightly 

 rostrate ends. L. 0,o55 to 0,075; B. (>,oi 2- 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. Striae 9 in 0,oi mm., parallel, radiate at the 

 ends, punctate; puncta coarse, forming longitudinal rows, 14 in 0,oi mm. — PI. If. 10, 11. 



]\larine: Balearic Islands! Ceylon! Labuan! Japan (Brun Coll.)! 



Diploneis Em;, (isiu). 



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 fnrroics. of nu)re or less breadth. 

 Structure: transverse finer stri;e, or coar.ser costa', which usually continue in a 

 rudimentary state across the furrows, where they fre(|ueutly give rise to a longi- 

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

 more longitudinal costfie., giving the valve the appearance of being reticulated; or 

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

 .4 D. f>(sc((, D. Smith ii, D. flidi/ina, D. fmbcinda, D. chersoyiensis and 1). constrict a) 

 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 orbicixlar small discs. 

 'f The name Diploneis was gi\eii l)y Ehrenbbrg 1840, to some panduriform 



"^ naviculoid diatoms. This characteristic is of no importance; but on the other 



Diploneis Snuthn. \^^Y\^\ the central nodule, the furrcnvs and the structure are so peculiar, that the 



times niagiuneu. . ^ 



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. nitesccns. The horns correspond evidently to the lyre-shaped expansions or 

 lateral areas in the section of Navicuhe Lyratre, 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. Di})!- hifalina Donk. and D. Hudsonis Urun. 

 Outside the horns are depressed parts of the valve, furroivs. These furrows have usuall}' a longi- 

 tudinal row of large pearls, formed by the continuation of the costffi 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 IuhhUi, 

 of different structure from the outside part of the valve. Such lunula; occui in 1). mirahilis, D. 

 Crabro and others. 



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

 has fine striiE, which in I). Hndsonis are formed by oblicjuely decussating puncta. In other forms 

 there are coarse costa', not comjiosed of puncta. The costit 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 costte 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 costre. A similar structure 

 occurs in Scoliofropis and Goniphoneis. In the larger forms the transverse costai alternate with 

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

 valve. In />. Cmlhro and allied forms these ocelli form a marginal row, which in the middle ap- 



