168 p. T. CLEVE, SYNOPSIiS OF THE NAVICULOID DIATOMS. 



Totarfe Diatomiste II PI. VI f. 5. As Campyoneis notahilis Brdn has described a form from Ro- 

 driguez, which, to judge from the figure seems not to dift'er essentially from C. GrerilUi. 



Cocconeis (Eiib.) Cl. 



Valve in oiitline broadly elliptical. Upper valve ecostate, with a more or less narrow longitu- 

 dinal axial area. Structure: puncta or alveoli arranged in transverse and, frequently, longitu- 

 dinal rows. Lower valve usually with a marginal line or marginal area. Between the valves is 

 a more or less rudimentary, loculiferous annulus. Frustules usually bent along the longitudinal 

 axis. Cell-contents (of C. Pediciih(s) a single chromatophore-plate, along the inside of the upper 

 valve, lacerate at the margin and with a deep sinus from the margin to the centre, where the 

 nucleus is embedded in the central plasma-mass (Pfitzeh. Ban u. Entw. p. 87). In conjugation 

 two cells split at the lower valve and secrete a voluminous gelatinous mass, inside which is 

 formed a large globular auxospore, the exospoi'iura of which is hyaline and without ribs. The in- 

 terior of the auxospores contains a lacerate endochrome-plate (Bqrscow: Siissw. Bac. p. 97). 



This genus comprises the most common species of the old genus Cocconeis. The obsoletely 

 loculiferous rim indicates that these species are akin to Mastogloia, probably degenerated forms of 

 that genus. In several forms of C. ScnieUnm the rows of puncta end near the margin in short 

 double rows of smaller puncta, as is also the case with Masfogloio, (Orfhoneis) splcndida. 



All these forms, C. gihhocalyx perhaps excepted, live attached to algte aiul other objects 

 in the water by the lower valve. 0. Placenfula, (J. Pcdiculns and C. Discnlus live in fresh, but 

 also, especially C. Fedic, in brackish water. The other species are marine, but C. Scutellum 

 also occurs in brackish water. 



{ 



Artificial key. 



Median line sigmoid C. niistralis Pet. 



— straight 2. 



I Axial area of the upper vulve lanceolate 3. 



' \ — — — — • — linear 4. 



._, j Area very broad. Marine C. grata A. S. 



\ — moderately broad. Freshwater liabitat C. Disculus Schum. 



. j Upper valve finely striate 5. 



I — • — with coar.se puncta or alveoli 6. 



^ J Upper valve with a marginal line C. Placcntula Ehb. 



■ ■ \ — — without C. Pediculus Ehb. 



. j Upper valve coarsely reticulate C. Van Heurrkii Cl. 



' \ — — — punctate ' 7. 



j Margin of the upper valve finely striate 8. 



\ - - - - not — 9. 



J Rows of puncta in the upper valve 4 to 5 in 0,oi mm C. granulifera Grun. 



■ \ — — — — — 8 to 9 — — C. cruciata Pant. 



I Valve lanceolate C. gihhocalyx Brun. 



I — elliptical 10. 



Puncta of the uj)per valve forming equidistant transverse and (usually) 

 10. { straight longitudinal rows C. Scutellum Ehb. 

 — — not — — — — C. distans Greg. 



1. (". granulifera Grev. (18fil). — Outline elliptical, with broad, rounded ends. L. 0,o28 

 to 0,05 7; B. 0,0 18 to 0,038 mm. Upper V. with finely striate margin (stria? 17 in 0,oi mm.), 

 narrow axial area and radiate rows (4 to 5 in 0,oi mm.) of large puticta (about 5 in each row). 

 Lower V. with finely striate margin (striai 20 in 0,oi mm.). Axial area indistinct; central area 

 small rounded. Median line sti-aight, reaching to the margin. Strife about 13 in 0,oi mm. strongly 



