PROTOZOA. 151 



(memos, one; ihalamos, chamber), includes those Rhizopoda which are inclosed in a 

 single shell, and have a minute opening for the extrusion of the filamentous pro- 

 cesses by which motion is effected. The Sub-class Polythalamia includes those hav- 

 ing calcareous shells, consisting of a series of distinct chambers, which sometimes 

 communicate with each other, and at other times appear to be completely closed 

 up. Each chamber is supposed to contain an independent animal, though the indi- 

 vidual animals may be so connected, through the openings communicating between 

 the cells, as to constitute a common mass. In some genera each chamber presents 

 only a single external opening, but in most genera the substance of the shell is 

 pierced by minute pores, like a sieve, through which delicate filaments, are pro- 

 truded. 



The Order Radiolaria (radiolus, a litle ray,) includes many beautiful forms, liv- 

 ing and swimming in vast multitudes near the surface of the ocean. Most of them 

 have a complex silicious skeleton of great beauty of form and symmetry, and after 

 death the skeletons sink to the bottom of the ocean, where they often furnish the 

 chief part of the mud. On the island of Barbadoes, Tertiary strata 1,100 feet in 

 thickness, consisting of marls, tripoli, and ferruginous sandstone, are largely com- 

 posed of the silicious skeletons of Radiolaria. The iNicobar Islands of the Indian 

 Archipelago, consisting of clays, marls, and arenaceous marls, to the extent of 

 2,000 feet in thickness of Tertiary age, are largely composed of the remains of this 

 Order. 



The Order Foraminifera (foramen, an aperture; fero, I bear,) includes all the 

 families of Palaeozoic Rhizopoda noticed in this work. They are marine shell- 

 bearing animals, living at the bottom of oceans and seas, attached, free, or pelagic, 

 and swimming on the surface of the water, from whence their dead shells form an 

 incessant rain to the bottom of the ocean. They are generally microscopic, though 

 a few are several inches in diameter. Some extinct genera are much larger than 

 any of the living forms. Prof. Leidy obtained 18,700 shells of a single species of 

 Nonionina from an ounce of mud scraped from the surface, between tides, at At- 

 lantic City. In another sample, from Cape May, he obtained 38,400 shells; and 

 in an ounce from the bathing beach at Newport, Rhode Island, he estimated there 

 were 280,000 shells of several genera and species. The sediment of the Atlantic 

 Ocean is so largely constituted of one kind of foraminiferous shell, that it is gener- 

 ally called Globigerina ooze. Common -chalk is almost wholly composed of the 

 shells of Foraminifera. The building stone of the city of Paris is almost wholly 

 made of the shells of Foraminifera belonging to the Sub-order Miliola. The Nutn- 

 mulite limestone of different countries is composed of foraminiferous shells, and so 

 is the Fusulina limestone of Carboniferous age. The microscopic genera and species 

 of the Palaeozoic rocks have not been much studied. The classification of the Pa- 

 laeozoic Foraminifera, so far as they have been investigated, is as follows : 



Family Calcispjlerid^e. — Calcisphaera. 



Family Eozoonhle. — Eozoon. 



Family FusuLiNirxaa. — Fusulina, Loftusia, Moellerina. 



Family Globigerinid^. — Calcarina. 



Family LituolidjE. — Endothyra, Nodosinella, Valvulina. 



Family Affinity, uncertain. — Rhabdaria. 



