20 LOWER INVERTEBRATES. 



3. Forms in which the inferior aperture is single and relatively small, but supple- 

 mented by conspicuous orifices on the superior surface of the shell, as in Qlobigerina 

 rubra. 



Besides these, there are forms represented under the generic name Orbulina, which 

 seem properly to belong to the Globigerinm as sub-generic forms. Orbulina has a 

 spherical shell, usually without a definite mouth, but provided with two sets of perfo- 

 rations diSering in size, — one series numerous and minute, the other larger and less 

 numerous. 



Closely allied to the Globigerina, if not properly belonging to that family, is the 

 beautiful Hastigerina murrayana, found by the " Challenger " expedition. This organ- 

 ism was found long ago by D'Orbigny (1839), and described by him as Nonionina 

 pelagica, and was one of the first Foraminifera taken at the surface of the sea. 



The Foraminifera inhabit the sea, and their remains are gi-adually forming rocky 

 strata on the ocean-bed, in all respects like the chalk of the cretaceous period. For a 



long time it was supposed that the ForamiuLfera 

 found at the bottom of the sea passed their entire 

 Ufe there. Prof. "Wyville Thomson held firmly 

 to that opinion until the results of collections with 

 the tow-net at the surface conclusively proved that 

 many of them live near the surface. It is now 

 known that a few species of Globigerina inhabit 

 the superficial waters, but a far greater number 

 pass their life at the bottom. 



The pelagic forms of Globigerina are usually, 



rig. 19.— Helixostegine forms of Foraminifera. , , . mi t t ,. 



but not always, spmous. The long, delicate spines 

 are somewhat flexible, and clothed with granular streaming sarcode ; and for some 

 distance from the shell the frothy sarcode fills the spaces between them. The spines 

 are so delicate that a mere touch will break them off, and spinous shells are never 

 seen in material brought up in the dredge. Sometimes the spines are very long ; in 

 Hastigerina murrayi the spines are fifteen times the diameter of the shell, and the 

 frothy, alveolar sarcode extends outward between the spines to a distance equal to twice 

 the diameter of the shell. 



The Globigerina are so abundant in some places, and their remains constitute so 

 large a proportion of the shiny calcareous ooze covering a great part of the sea-bottom, 

 that the ooze has long been designated " Globigerina ooze." The Globigerina ooze 

 consists of the remains of Globigerina and Orbulina in great abundance, with a smaller 

 proportion of the genera Pullenia and Sphoeroditia, Avith occasional specimens of Has- 

 tigerina, together with remains of radiolarians, diatoms, and some cm-ious structures 

 known as rhabdoliths and coccoliths, the nature of which is not )-et understood. 



As regards the distribution of the remains of protozoic life over the ocean-floor, it 

 appears that the Globigerina ooze extends from four hundred down to about two thou- 

 sand fathoms. Beyond this limit there seems to be a gradual disintegration and solution 

 of the calcareous substance of the shells, resulting first in a gray ooze down to two thou- 

 sand three hundred fathoms, containing no perfect shells, but some calcareous matter 

 effervescing with acids, finally changing as we go still deeper to an impalpable red 

 feldspathic mud, or " red clay," as it has been termed, which covers vast areas. The 

 red clay is supposed to be derived partly from the disintegration of the shell-matter of 

 the gray ooze and the solution of the calcareous portions, and partly from the mineral 



