In the shallower tropical waters, especially on the central ridge, considerable areas are covered by Pteropod ooze, a deposit consisting largely of the shells of pelagic molluscs.
The eupelagic deposits are subdivided by Kriimmel into two main groups; (a) epilophic,' including the pteropod, globigerina and diatom oozes occurring on the rises and ridges and in the less deep troughs.
The floors of the Caribbean, Cayman and Mexican Basins in the Central American Sea are covered with a white calcareous ooze, which is clearly distinguished from the eupelagic pteropod and globigerina oozes by the presence of abundant large mineral particles and the remains of land plants.
To this inconceivably slowly-growing deposit of inorganic material over the ocean floor there is added an overwhelmingly more rapid contribution of the remains of calcareous and siliceous planktonic and benthonic organisms, which tend to bury the slower accumulating material under a blanket of globigerina, pteropod, diatom or radiolarian ooze.
Pteropod ooze is merely a local variety of globigerina ooze in which the comparatively large but very delicate spindleshaped shells of pteropods happen to abound.
These shells do not retain their individuality at depths greater than 1400 or 1500 fathoms, and in fact pteropod ooze is only found in small patches on the ridges near the Azores, Antilles, Canaries, Sokotra, Nicobar, Fiji and the Paumotu islands, and on the central rise of the South Atlantic between Ascension and Tristan d'Acunha.
kilometres - about two-thirds of that in the Atlantic. Pteropod ooze occurs only in the neighbourhood of Fiji and other islands of the western Pacific, passing up into fine coral sands and mud.
Other Lamellibranchs exhibit either a trochosphere larva which becomes a veliger differing only from the Gastropod's and Pteropod's veliger in having bilateral shell-calcifications instead of a single central one; or, like Anodonta, they may develop within the gill-plates of the mother, though without presenting such a specialized 210 1P -' 1 °* larva as the glochidium.
C, Veliger of a Pteropod showing p, Foot.
Other Lamellibranchs exhibit either a trochosphere larva which becomes a veliger differing only from the Gastropod's and Pteropod's veliger in having bilateral shell-calcifications instead of a single central one; or, like Anodonta, they may develop within the gill-plates of the mother, though without presenting such a specialized 210 1P -' 1 Ã‚°* larva as the glochidium.
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