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Rh perforated. Any arrangement more truly unnatural can scarcely be conceived:—to me it appears a sort of reductio ad absurdum of the principle that the unilocularity or multilocularity of the shell should be held of primary account in the systematic arrangement of the organisms in question.

An important step in the classification of the was made by the late Prof. Johann Müller, in his admirable memoir (Transactions of the Berlin Academy, 1838), "Uber die Thalaasicollen, Polycystinen, und Acanthometren des Mittelmeeres;"' these three groups, whose mutual affinity he showed to lie very strong, being associated by him into a distinct sub-class, which he distinguished as. He failed, however, to perceive what appears to me to be the essential relationship between the Acanthometrina and Actinophryna; an Acanthometra, as we shall presently see, being nothing else than an Actinophrys furnished with a siliceous skeleton. And in drawing a strong line of demarcation between the simple and the composite forms of Thalassicolina, he endeavoured to establish a distinction which seems to me untenable among animals that multiply by gemmation, between the simple and the composite forms. Taking the group of as a whole, however, it may be considered an eminently natural one; and I adopt it as one of the primitive sub- divisions of the class, adding to it the family Actinophryna, which includes Actinophrys and its immediate allies, for reasons which will be presently apparent.

More recently an attempt has been made to frame a natural classification of the as a whole, by two distinguished pupils of Prof. Müller, MM. Claparède and Lachmann ("Études sur les Infusoires et les Rhizopodes," Genève, partie 2ième, 1859); and it is with some diffidence that I venture to express a divergence of opinion from observers who have been trained in so excellent a school, and who have given such ample proofs in their published writings of practical familiarity with the several forms whose relations they discuss. The following is the scheme proposed by them (l.c. p. 434):—