STILL FOUND IN A LIVING STATE. 323 
labour, been reduced to a general classification and definition of 
forms welcome alike to zoology and to geology. Among the 
very numerous, clearly defined, and frequently large forms of the 
genus, it is only some smaller, delicate, and less sculptured ones 
which stand in connection with living species. 
Moreover, in 1836, Desmoulins and Grateloup* determined 
several species of Echinidz in the (anomalous) chalk of Dax as 
being identical with now living species, specimens of which were 
in Desmoulins’ collection. Agassiz, the most ingenious and 
latest systematic observer of the Echinidz, has expressed him- 
self decidedly against these observations. The Jatter asserts, 
that there are neither fossil fish nor fossil Echinide known to 
him that really belong to still existing species, and he published 
this declaration expressly with a view to these observations of 
Dax, 1838+. Bronn only remarks in answer to this, that 
nevertheless the identity of the species is not inconsistent with 
the history of the development of the earth; but he himself has 
not published any further confirmations or observations. 
In December 1838, I made known to the Academyt that 
there had been found from five to six species of Infusoria in the 
chalk, which appeared so similar to the still existing forms of 
the present world, that they did not present any character clearly 
distinct ; consequently it was not possible to give them any 
different names. They are,— 
Eunotia Zebra, 
Fragilaria rhabdosoma, 
Fragilaria striolata ? 
Gallionella aurichalcea, 
Navicula ventricosa, 
Synedra Ulna. 
The Synedra Ulna I had already recognised and specified, in 
1837, in the Polirschiefer, or Chalk-marl of Oran; there, also, 
was found the more distinct Navicula ventricosa. Eunotia Zebra 
was from a Greek marl, in which, at the same time, calcareous- 
shelled Polythalamia of the white chalk appeared. The Gallionella 
_ durichalcea was from the decided white chalk of Riigen. Both 
_ the Fragilarig were from the decided white chalk of Gravesend. 
* Memoir on the Echinides of Dax, 1836-38. See Bronn’s Lethea, ii. p. 
771, 1838. + Bronn’s Lethea Geogn., ii. p. 771, 1838. 
t Transactions of the Academy of the year 1838, pp. 85, 91 seg., and p. 149, 
in the tabular conspectus at the end. Separate edition: on the formation of 
the chalk, &c., pp. 29, 35, and at the end. 
