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XXVIII. Description of Parkeria and Loftusia, two gigantic types of Arenaceous Fora- 
minifera. By William B. Carpenter, M.D., V.P.B.S., and Henry B. Brady, 
F.L.S. 
Received March 18, — Read April 22, 1869. 
Introduction. 
In the “ Concluding Remarks ” appended to Part II. of my “ Researches on the Fora- 
minifera ” (Philosophical Transactions for 1856, p. 565), I pointed out that the System 
of Classification of that group which had been erected by M. D’Orbigny on the exclu- 
sive basis of plan of growth , was inconsistent with the facts disclosed by a careful study 
of the organization of the five typical Genera described in my first and second Memoirs : 
since it had the effect of bringing together Genera whose strongly marked physiological 
differences required that they should be separated by the widest possible interval ; whilst 
it ranked under different Orders generic types which exhibit the closest physiological 
relationship. And I then laid it down as a fundamental principle, “ that physiological 
conformity in the condition of each individual segment, as indicated by the structure of 
its shelly investment , is a character of primary importance; whilst the plan of growth, 
that is, the mode of increase in the number of chambers, is a character of subordinate 
importance.” And in the “ Concluding Summary ” appended to Part IV. (Philosophical 
Transactions, I860, p. 569), I further expanded this doctrine, by showing that all the 
types which I had described might be ranged in two parallel Series : one of them cha- 
racterized by that peculiar texture of the Shell which had been appropriately designated 
Porcellanous by Professor W. C. Williamson*; whilst the shell-substance of the other 
has the texture which had been described by the same excellent observer, with equal 
appropriateness, as Hyaline or Vitreous. A third type of Shell-structure had been noticed 
by Professor W. C. Williamson (loc. cit .) under the designation Arenaceous ; the shell 
being mainly formed, not by a calcareous exudation from the sarcode-body of the animal, 
but by the aggregation of particles of sand obtained from without, the cement by 
which these are attached together being all that the animal supplies. These differences 
in the character of the Shell were regarded by Professor W. -as indicative of “ physiolo- 
gical differences in the living sarcode, or secreting animal substance, that have at least 
a specific value but while expressing (p. xix) a strong opinion as to the unphiloso- 
phical nature of M. D’Orbigny’s System, he did not propose any substitute for it ; 
and contented himself with ranking porcellanous , vitreous , and arenaceous shells that 
correspond in general form, as distinct Species of the same genus. 
The Arenaceous type having been made an object of special study by Messrs. Parker 
* “ On the Recent Foraminifera of Great Britain,” Introduction, p. xi. 
5 D 
MDCCCLXIX. 
