340 PROF. EHRENBERG ON ANIMALS OF THE CHALK 
hid under the shell. In both forms, however, the animal contents 
of the minute shells, which are also more transparent and clear 
in their structure than the fossil, have been placed beyond doubt. — 
In my former memoir on the formation of chalk by micro- 
scopic animals, four species were arranged among the calcareous 
animalcules of that deposit, with a mark of doubt as to their 
being identical with living species, and an apology for the uncer- 
tainty from a want of knowledge of living specimens. They 
were Globigerina bulloides, D’Orbigny ; Globigerina helicina, 
D’Orbigny; Rosalina globularis, D’Orbigny; and Textilaria 
aciculata of the same observer. With respect to the last species, — 
I now entirely withdraw my doubt after these recent observa- 
tions, and assert the forms of the chalk and of the present day 
to be identical ; nor do I any longer think I require an excuse, if 
I likewise admit the other three as forms actually belonging to 
species of the present world, since a second fossil species could 
really be observed in a living state. 
Thus, then, (microscopic) calcareous-shelled animalcules of 
the chalk still exist in a living state; and the whole number of 
the forms at present found to be identical* is according to ob- 
servation 15, but probably to be provisionally fixed at 18 or 20,viz. 
13 siliceous-shelled animalcules, 2 Xanthidia of the flint (Xanth. 
furcatum, and hirsutum), and 5 calcareous-shelled animalcules ; 
at the same time, the circumstance should be well noted, that 
many of these forms are exactly those of which the mass is com- 
posed, consequently the most numerous in individuals of the chalk 
formation, and not the more rare, which appears to lead to a 
settlement of the still existing physiological difficulties. 
VIL. Explanation of the Organization of several Polythalamia of 
the North Sea observed alive in Berlint (Jan. 16th, 1840). 
An external animal, having the form of a Sepia, and which 
bore the minute shell frequently resembling a Cornu Ammonis: 
as an internal bone in the back, had Te years ago, after di- 
ligent observation, been ascribed by D’Orbigny to the Poly-) 
thalamia, whose very minute and often microscopic calcareous 
shells constitute in inconceivable numbers, and in now a 
[* Mr. E. Forbes (Feb. 1842) remarks as to the results of his dredging in 
the Adriatic, ‘‘ Strange to say, the most characteristic shells in those depths are 
species known only in a fossil state hitherto.”— Annals of Nat. Hist., No. 57, 
for May 1842.—Ep. ] 
+ Report of the Academy, Jan. 16th, 1840. Sce note in preceding page. 
