RECENT RESEARCHES IN THE DIATOMACEiE. 89 



relation to one another, as in the case of Scoliopleura, as 

 also by the two accompanying longitudinal striae. It has 

 only a single endochrome-plato, lying on one girdle-band, 

 and with its margins reaching to the valves; fission takes 

 place from the ends throughout. A central plasm-mass is 

 obvious. Whether the similarly keeled genera, Amphiprora 

 (Ehr.) and Donkinia (Pritch.), belong to this or to the pre- 

 ceding group remains to be determined. Auxospores in all 

 these forms are still unknown. The concluding observation 

 of our author suggests the propriety of subjecting the 

 various related forms to a careful examination, with a view 

 to a satisfactory arrangement. 



Nitzschiem (Grun.). 



The forms hitherto treated of agree in this particular, 

 that, with the exception of the Epitheniiece, which have a 

 very indistinct median line, they exhibit nodules and dis- 

 tinct median lines ; and that the transverse section is rec- 

 tangular or trapezoid, except Encyonema, in which case 

 it is slightly rhomboid. The Nitzschiece, on the contrary, 

 possess neither nodules nor median lines, and besides, their 

 transverse section is ever distinctly rhomboid. This group 

 embraces three genera, Nitzschia, Ceratoneis, and Bacil- 

 laria. 



Nitzschia. 



In which we have species of a twofold structure, which 

 may be distinguished as similarly striate (gleichriefige) and 

 alternately striate (wechselriefige) . The valves of every 

 Nitzschia exhibit on one margin a row of nodulated thick- 

 enings, called keel-puncta, Avhich are situated in the two 

 valves either on the same or on opposite sides. All the 

 NitzschiecB examined possess a central granular plasm-mass, 

 in which a large nucleus may be distinguished, as also 

 a single endochrome-plate, either completely interrupted in 

 the middle, or nearly so by an elliptical opening. 



The endochrome-plate in the case of the similarly striate 

 Nitzschiece, so far as the author has been able to investigate 

 {N. elongata (Hantzsch), N. flexa (Schum.), lies on one 

 girdle-band, and that the one which stands more remote 

 from the keel-puncta; it then covers the valve, and with 

 small folds extends to the opposite girdle-band. Some of 

 the alternately striate Nitzschiece — for example, N. palea 

 (Kiitz.J, W. Sm., N. sigmoidea, W. Sm.,iV. Clausii, Hantzsch 

 — present the same position of the endochrome-plate, while 

 N. dubia, Hantzsch, and N. linearis (Ag.), W. Sm., differ 

 widely in the inner structure. In them the endochromeT 



