144 SKETCH OF THE INFUSORIA 



self of the oxistonce of six openings in K viridis, (see rennarks 

 (•oiu'crnini? lliat species,) and with regard to the species ever 

 forming chains, 1 can state that it is not rare to meet with four, 

 souictinics oven eight uniled laterally. I have even seen them 

 ihns nulled in llio fossil state. 



a. Havin"' transverse stria^, (internal cells,) subgenus Surirella. 



Navicula viridis. (PI. II, fig. 16, a, b.) Striate, carapace straight, 

 lateral faces truncate at the ends, ventral faces rounded at the ends, 

 fifteen stria\ (cells) in x^o of a line. Length, ^^ to one sixth of a 

 hnc. 



This beautiful species is one of the largest and most abundant, 

 both in the recent and fossil state. It occurs all over Europe, and 

 is equally diffused in this country. I have myself observed it in 

 Maine, Massachusetts, New- York, Ouisconsin and Virginia. It 

 is easily recognized by means of its large size and beautifully 

 marked ventral faces. The striae seen on these faces may coi'- 

 rcspond to internal cells, but I believe them to be linear openings 

 in the carapace itself, as may easily be seen on the fragments of 

 fossil specimens. There are three rounded spaces on each ven- 

 tral face, which I think have been mistaken for openings, but 

 which appear to me to be thicker portions of the carapace. One 

 of these spaces is in the middle, and the other two at the extremi- 

 ties of the stiiated surfaces, and they ai'e connected by a very 

 delicate double line (canal ?) A similar structure is seen on sev- 

 eral other species of Navicula, Cocconema and Gomphonema. 

 The real orifices are shown at c, c, c, c, in our fig. 16, b. INIoving 

 particles somewhat like those of Closterium may sometimes be 

 seen near the extremities. In fig. 17, a, b, PI. II, I have copied 

 from Ehrenberg, (Die Fossilen Infusorien und die lebendige 

 Dammerde, Berlin, 1837, PI. 1, fig. 19,) a sketch in which he 

 represents' the organs of motion, the stomach, &c. of this species. 

 The reference letters having been omitted by the engraver of 

 Ehrenberg's plate, I have been obliged to insert them according 

 to what I believe was their intended position. 



The following is a translation of Ehrenberg's explanation of 

 this figure. (See fig. 17, PI. II.) 



" A living specimen of Navicula viridis in which by the injec- 



