FOEAMINIFERA OF NORTH PACIFIC OCEAN. 3 



seemed to prove the contrary in regard to many species. With the 

 lines of demarcation of species more closely drawn, it will be apparent 

 that certain of them have well-defined areas of distribution and are 

 found only between certain bathymetric altitudes. Not only is this 

 true in regard to species, but various species form definite faunas, as 

 will be later discussed. With plenty of specimens for comparison 

 from different areas it is fairly easy to show the specific differences 

 and the actual amount of the variation. 



Throughout the group of the Foraminifera there is a nearly com- 

 plete series, from a simple gelatinous covering of the cell in some of the 

 fresh-water forms to the complex calcareous test of the higher groups. 

 The fresh-water forms, while not considered in the systematic part of 

 the present work, are nevertheless of especial interest on account of 

 their primitive characters. In Myxotheca the simplest sort of cover- 

 ing is found, a gelatinous test which is flexible, so that it takes the 

 shape of the changing form of the cell. There is here also no definite 

 aperture, the pseudopodia being pushed through at any point. In 

 others of the fresh-water forms the test may be of flexible chitinous 

 material, but has a definite shape when the animal is at rest and usually 

 one or more definite and permanent orifices. 



In the marine species, which form the basis of the present work, 

 there is usually a definite, specific form to the test and the aperture is 

 permanent. The materials used in making the test may be grouped 

 in two classes, (1) those derived from foreign sources, and (2) those 

 secreted by the animal itself. The foreign materials are derived from 

 the bottom on which the animal lives, and therefore even in the same 

 species found under different conditions there is some variation in the 

 character of the materials used. In general, however, there seems to 

 be a certain amount of selective power on the part of certain forms, 

 and such characters have been used as of generic rank in systematic 

 work. The foreign material most frequently used is the mud or sand 

 of the ocean bottom, but certain forms use sponge spicules, either 

 making them into a soft felted mass {Pilulina) or arranging them in a 

 definite manner and firmly cemented ( Technitella) . Other foraminif- 

 eral tests may be used, as may various small bodies which come 

 within the range of the animals. The cement in the agglutinated 

 tests may be chitinous, of iron oxide, or calcareous. 



Of these calcareous tests two sorts have been recognized, one with 

 a definite aperture or series of apertures and with minute pores (the 

 perforate group) , the other with a definite aperture or series of apertures 

 but without minute pores (the porcellanous group) . By many writers 

 the latter group, represented by the Miliolidae, has been held to be 

 primitive and a group which had not developed perforations. On the 

 other hand, certain evidence, such as the perforate condition of the 

 early chamber of Peneroplis and other genera, would indicate that they 



