ORDERS OF RIIIZOPODS— FORAMINIFERA. 15 



seas, some attached, but generally free, and creeping 1 on the surface of sea- 

 weeds, on the mud, the sands and rocks, or on dead shells ar.d corals, or 

 the lifeless fixed hard parts of other living animals, as the shells of mollusks, 

 corals, sertularians, and sponges. Large numbers are pelagic, or live on 

 the high seas, swimming in the superficial water, while their dead shells 

 form an incessant rain, and contribute largely to the formation of the ocean 

 mud. 



Of their class, the Foraminifera have been longest and best known, 

 and their tiny and beautiful shells have been the subjects of many descrip- 

 tions and illustrations. The characters of ihe order have been especially 

 elaborated in more recent works, among which may be mentioned the 

 "Organization of the Polythalamia" by Dr. Max S. Schultze, and the 

 "Introduction to the Study of the Foraminifera" by Dr. William B. Car- 

 penter. 



The Foraminifera, though generally too minute to be distinguished by 

 the naked eye, are readily detected with a good pocket-lens. They are 

 commonly largest in tropical seas, and even the same species are better 

 developed in warmer than in colder latitudes. A few, the giants of their 

 kind, are conspicuous for their size, and range even to the diameter of seve- 

 ral inches. In former ages they frequently reached a greater growth, so 

 that fossil forms are commonly larger than those now living. Some of the 

 extinct species exceed in size double that of any known existing ones. 



The Foraminifera are provided with a shell, mostly calcareous, but 

 often partially calcareous with incorporated siliceous sand, or it is composed 

 of sand-grains alone cemented together. With few exceptions, the shells 

 are partitioned into many chambers, and trie most common forms, which 

 are spiral, so nearly resemble the shells of the Nautilus and Ammonite, that 

 until a comparatively late period all were classed together as Polythalamia 

 (Gr. polus, many; thalamos, chambei*) or Cephalopoda (the Cuttle-fishes). 

 D'Orbigny, recognizing in the shells of the Nautilus and Ammonite that the 

 chambers were traversed by a tube, while in the shells of the so-called 

 microscopic Cephalopods the chambers communicated by one or more holes, 

 called the former Siphonifera {siphon, a tube; fero, I carry) and the latter 

 Foraminifera. In a systematic arrangement of the Cephalopods in 1825, 

 D'Orbigny still retained the Foraminifera as an order. Dr. Carpenter 

 remarks that "no suspicion appears at that time to have crossed the mind 



