Sketch of the Infusoria of the family Bacillaria. 95 



I select from the species of Coscinodiscus, described by Eh- 

 renberg, the following, as apparently identical with American 

 species from Richmond, Va. In connection with the description, 

 I give a reference to figures drawn by me from fossil American 

 species, long before Ehrenberg's characters for the species were 

 received. 



Coscinodiscus li?ieatus. (PI. 2, fig. 12, a, b.) Carapace marked 

 by small cells disposed in a series of parallel and transverse lines. 

 Found, fossil in the chalk marl of Caltasinetta, and in the live 

 pondition at the Cuxhaven. The cells in this species form par- 

 allel lines in whatever direction they may be viewed. In large 

 and well preserved fossil specimens, as many as twenty five 

 openings were seen near the circumference. Within the live 

 forms, numerous yellow vesicles are sometimes seen, as in Gail- 

 lonella. Diameter of fossil, yy^ijth to ^-^oth ; living tts (j^^^ 

 to g-g^oth. Fossil at Richmond, Ya. 



Coscinodiscus radiatus. (PI. 2, fig. 14.) Carapace large, 

 marked with cells of moderate size, disposed in lines radiating 

 from the centre. Towards the margin the cells become smaller 

 in size. Very abundant in fossil state at Oran, alive near Wis- 

 marand Cuxhaven, jj-nth to a-^-^th. Fossil at Richmond, Va. 



Coscinodiscus Argus, ( ? var. of C. radiatus.) Carapace with 

 large cells at the centre, and smaller ones at the circumference, 

 the order of the rays being often interrupted. 



Fossil at Oran and Caltasinetta in chalk marl, living in sea 

 water at Cuxhaven. The cells of the discs from Oran vary very 

 much in size. The ova are of a greenish color in the living 

 forms, which are very rare. Diam. -g^joth to algth. Fossil at 

 Richmond, Va. 



Coscinodiscus oculus-ij'idis. Carapace marked with rather 

 large radiant cells, except near the centre and circumference, 

 where they are smaller. Some of the larger cells in the centre 

 form a sort of star. Fossil in the chalk marl of Greece : alive 

 near Cuxhaven. Diameter, ^i^. This large species is curiously 

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

 are apparently caUvSed 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. 



