96 Sketch of the Infusoria of the family Bacillaria. 



Coscinodiscvs patina. (PL 2, fig. 13, a. b.) Carapace large, 

 cells of moderate size disposed in concentric circles. Cells smaller 

 towards the circumference. Fossil in chalk marl of Zante, alive 

 at Cuxhaven. The young and vigorous specimens of live indi- 

 viduals are completely filled with yellow granules, whilst the 

 older ones have an irregular granulated mass within them. Di- 

 ameter, glcth to aifltli- Fossil at Richmond, Va. Our figure 

 shows a small specimen. 



Of the genus Actinocyclus, Ehrenberg describes several new 

 species, which have been found fossil in the chalk marls of Oran^ 

 Caltasinetta, &c., and living in sea water at Cuxhaven, Chris- 

 tiana and Tjorn. Several of these species have no partitions, 

 but have surfaces marked with minutely punctate rays. The 

 great variety which occurs among the forms of Actinocyclus, 

 found fossil at Richmond, leave no doubt in my mind, that all 

 of Ehrenberg's species will be found among them. I also be- 

 lieve that I have seen a living species of this genus, or of Cos- 

 cinodiscus, in the ooze of the Hudson River, near West Point. 



For Ehrenberg's characters for the new species, see Pritchard's 

 Hist. Inf., p. 428-429. 



Navicula. 



Free, separate or binary, carapace simple, bivalve or multivalve 

 [siliceous) having six [?] openings; never xmited in form of a 

 chain by perfect spontaneous division. 



On these characters as given by Ehrenberg for the genus Na- 

 vicula, I would remark that there do not appear to be any true 

 valves or parts capable of separation without fracture, although 

 each species will usually break along certain lines or edges into 

 a definite number of parts. I have not been able to satisfy my- 

 self of the existence of six openings in N. viridis, (see remarks 

 concerning that species,) and with regard to the species ever 

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

 sometimes even eight united laterally. I have even seen them 

 thus united in the fossil state. 



a. Having transverse strife, (internal cells,) subgenus Surirella. 



Navicula viridis. (PI. 2, fig. 16, a, b.) Striate, carapace straight, 

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

 fifteen strias (cells) in x^TT^h of a line. Length, -gJ^ to ^ line. 



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

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



