. The Earth beneath the sea : History . lOOii Fig. 5. Pteropods from a Recent sediment from the Tuamotu Archipelago. Fig. 6. Fish skeletal debris from a South Pacific zeolitic clay. than 500 m. The contribution of pteropods (and heteroiDods, which have some- what similar shells) to pelagic sediments is severely limited by the instability of their aragonitic shells. They are found more commonly in Mediterranean and Atlantic than Pacific sediments. This apparently reflects the shallower depth and more rapid rate of sediment accumulation in the former. F. Fish Debris Fragments of bone, placoid sc
. The Earth beneath the sea : History . lOOii Fig. 5. Pteropods from a Recent sediment from the Tuamotu Archipelago. Fig. 6. Fish skeletal debris from a South Pacific zeolitic clay. than 500 m. The contribution of pteropods (and heteroiDods, which have some- what similar shells) to pelagic sediments is severely limited by the instability of their aragonitic shells. They are found more commonly in Mediterranean and Atlantic than Pacific sediments. This apparently reflects the shallower depth and more rapid rate of sediment accumulation in the former. F. Fish Debris Fragments of bone, placoid scales and small teeth (Fig. 6) form a minor constituent of all pelagic sediments, but there has been no reported attempt to identify the fish they represent. G. Radiolaria Members of this group of Protozoa occur in all parts of the oceans, and contribute significant amounts of opaline silica to sediments, especially in tropical and temperate regions. Their tests, most of them 50-400 \l in diameter or length, exhibit a great variety of shapes generally based on spherical or helmet-shaped ground-forms (Fig. 7). In attempting to evaluate the literature on Radiolaria, it is important to bear in mind that there are two profoundly different, not closely related, groups of siliceous Radiolaria, and generalizations
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Keywords: ., bookcentury1900, bookcollectionbiodivers, booksubjectoceanbottom
