PROTOZOA. 



podial apertures, so that this division is not a strictly natural one ; but 

 the majority of forms included under this title have truly an imperforate 

 shell, and the name is one so long current and so widely used that it 

 seems unadvisable to entirely discard it. 



(W. B. Carpenter, Parker, and Rupert Jones, Introduction to the Study 

 of the Foraminifera, 1862 ; Max Schultze, Ueber den Organismus derPoly- 

 thalamien, 1854 ; H. B. Brady, Reticularian Rhizopoda of the Challenger 

 Expedition, Quart. Journ. Micro. Sci., 1879-81 ; Von Reuss, Entwurf 

 einer systematischen Zusammenstellung der Foraminiferen, Sitzungsb. K. 

 Akad. Wiss. Wien, 1861 ; Hertwig, Bemerkungen iiber die Organisation 

 und systematische Stellung der Foraminiferen, Jenaische Zeitschr. f. Natur- 

 wiss., 1876.) 



OKDER IV. RADIOLARIA. 



Sub-ord. 1. Cytophora. 



Fam. a. Acanthometrina. Acanthometra, Xiphacantha 



(fig. 5). 



Fig. 5. The skeleton of Xiphacantha, one of the Acanflwmetrina, greatly magnified. 

 (After Sir Wyville Thomson.) 



