180 Mr. C. Mereschkowsky on Scllapliora. 



described ; l)ut tlioy are easily to be (li.stini^uisbcd one from 

 anothor by the outlines of the valve, their siz^, their moie of 

 living, and from all other species of Navieuloid diatoms by 

 their inner structure. 



On account of the latter it seems to mo necessary to 

 cstablisli a now {renus, which I propose to call S'Uaphoni (or 

 "saddle-bearer"), as the endoclironie, consistin;;- of a single 

 chroniatophore-jilate, is placed on the diatom like a saddle 

 on a horse's back (PI. IV. tig. 12). 



The diagnosis of the genus is as follows : — 



SELLAPHORA, gen. nov. 



Valve small, symmetrical, linear to elliptical, with obtuse 

 ends, terminal nodules distant; stria) usually fine, connecting- 

 zone simple. Endochrome composed of one plate, resting 

 with its narrow median part on the surface of one of the 

 valves, with four long prolongations along the coimcctin^-- 

 zones. Pyrenoid absent. A few elseoplasts, sometimes 

 represented by two libroplasts *. 



The endochrome is very uniform in all the species, the 

 unique chromatophore-plate being always composed of two 

 parts — a narrow median part {m. in the figures) resting on 

 the surface of one of the valves, which may be called the 

 dorsal valve; and four long, usually narrow, linear prolonga- 

 tions, turned down at a right angle to the median part ami 

 resting on both connecting-zones (;?/'. in the. figures). The 

 diagram fig. 11 represents such a plate when spread out, m. 

 being the median part belonging to the valve and pr. the four 

 prol< ngatlons resting on the connecting-zone. The diagram 

 fig. 12 represents a transverse section of a fiustule and shows 

 the disposition of the plate in the frustule; the upper or 

 dorsal valve is provided with an endochrome ("«.)> the lower or 

 ventral valve is without one. 



I shall now describe the species belonging to this genus, 

 and then consider its affinities and its systematic position. 



* The elseoplasts are oil-drops usually applied to the clirouiatophores, 

 soniotiuies free, detaining tliis name as a general term, I have found it 

 necessary to divide the various forms of elaeoplasts into three classes, 

 as follows : — 



ffree, situated along the median 

 El.Teoplasts constant in | line, two or four in number . . libroplasts, 

 number and dispo- :! applied to tlie inner surface or to 

 sition: ( the margins of tlie chroniato- 



i phores, Irom two to four placoplasts. 



Elajoplaats variable in number and dispof-ition sparsio])lasts. 



