THE AMCEBAS 



3531 



of fine mud, slightly cemented, and lined inside by a smooth membrane; at the 



ends of the arms are large openings for the pseudopods; the diameter of the disc 



is about one-fifth of an inch, and that of the entire shell 



about half an inch; the animal lives in comparatively 



shallow water (about twenty fathoms), in the North 



Atlantic. Certain other sandy species are characterized 



by the regular form of their shells, which resemble those 



of calcareous species. The imperforate calcareous 



species are usually milk white. The shell possesses only 



one or a few apertures. The seedlet miliolina, previously 



referred to, is one of the commonest species; it has a 



world-wide distribution from the shore to three thousand 



fathoms. The terminal opening of the last and largest 



segment is guarded by a branched tongue-like process. 



The Miliolite Limestone of the Paris Basin is composed 



almost entirely of the shells of Miliolina and other 



Foraminifera. A considerable part of Paris is built of 



this stone, in which the tiny miliolinas can be distinctly seen with the aid of a lens. 



The porcellaneous Peneroplis forms a spiral, with a slit in the last-formed segment, 



through which the protoplasm of the body can be extruded. 



Peneroplis pertusus. 



a. lateral view ; b. Front view. 



(Magnified.) 



Orbitolites. 



a. From above ; b. Transverse section (natural size); c. Diagrammatic figure of section of Orbitolites complanatus 

 illustrating the transition from the simplest to the most complex type of structure. 



Orbitolites, one of the Imperforata, forms discs from one to two inches in 

 diameter. The shell is composed of a central coiled chamber, followed by concentric 



