INFUSORIA. 
71 
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 species. 
Coscinodiscus patina. (PL 2, fig. 13, a, b.) Carapace large; cells of moderate size, dis¬ 
posed in concentric circles. Cells smaller towards the circumference. Fossil in chalk 
marl of Zante ; alive at Cuxhaven. The young and vigorous specimens of live indivi¬ 
duals are completely filled with yellow granules, whilst the older ones have an irregular 
granulated mass within them. Diameter, s^oth to aLoth. 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 Cuxha¬ 
ven, Christiana 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 believe that I have seen a living species of this 
genus, or of Coscinodiscus, in the ooze of the Hudson river, near West-Point. 
For Ehrenberg’s character 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 united in form of a chain by perfect spontaneous division. 
On these characters as given by Ehrenberg for the genus Navicula, 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 myself 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 stria:, (internal cells.) Subgenus Surirella. 
Navicula viridis. (PI. 22, Fig. 16, a, b.) Striate, carapace straight, lateral faces truncate at the ends, 
ventral faces rounded at the ends, fifteen strias (cells) in y|oth of a line. Length to i 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 is equally diffused in this country. I have myself 
observed it in Maine, Massachusetts, New-York, Ouisconsin and Virginia. It is easily re¬ 
cognized by means of its large size and beautifully marked ventral faces. The striae seen on 
these faces may correspond 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 ventral 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 extremities of the striated surfaces, and they are connected 
