OF THE FAMILY BACILLARIA. 143 



near Cuxhaven. Diameter, ^tt)- This large species is curioilsly 

 marked, whilst under the microscope, with colored rings, which 

 are apparently caused by the peculiar arrangement of the cells. 

 There are generally from five to nine large cells at the centre. 

 Specimens are found in the infusorial stratum of Richmond, Va., 

 which have the star-like centre and probably belong to this spe- 

 cies. 



Cosciuodisciis patina. (PL II, 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, g^jy to ^i,7 of a line. 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- 

 tiaria 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 fovmd among them. I have also 

 seen living species of this genus, and of Coscinodiscus, 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-^29. 



Navigula. 



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

 (siliceous) having- six [?] openings; never united 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- 



