142 SKETCH OF THE INFUSORIA 



may 1)1^* shown as tlic cliicf forms met with in the chalk marls 

 of Sicily, and also that the species of the clialk formations are yet 

 to be found, as crowds of living creatures in the waters of our seas. 



1 select from the species of Coscinodiscus, described by 

 Ehrcnberii;, the following, as apparently identical with American 

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

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

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

 received. 



Coscinodiscus lineatus. (PI. II, 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 

 condition at 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, txVtt to ^i^; living, ttVtj to ^. 

 Fossil at Richmond, A^rginia. Living in New- York harbor. 



Coscinodiscus radiatus. (PI. II, 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 the fossil state at Oran, alive near Wis- 

 mar and Cuxhaven, ^ to ^ of a line. Fossil at Richmond, 

 Va. Living in New- York harbor. 



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, hving 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 hving 

 forms, which are very rare. Diaiu. -gi^ to ^^ of a line. Fossil 

 at Richmond, Virginia. 



Coscinodiscus ocidus-iridis. 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 



