444 Annals New York Academy of Sciences 



Braarud'^ and others have experimented on variation in salinity and its 

 influence on the growth of the coccolithophorids, Hymenocaras carterae and 

 Coccolillnis liuxleyi. For the tirst species, salinity was excluded as an important 

 environmental influence on growth. This corresponded to the littoral habitat 

 in which it is most abundant and in which salinities are quite variable. The 

 second species, C. huxleyi, is distributed worldwide in oceanic waters (35 per 

 thousand)" and in northern European coastal waters (15 to 20 per thousand). 

 Experiments have shown that between these ranges of salinity there was good 

 growth. 



Salinity apparently does act as an ecologic fence in excluding C. huxleyi 

 from brackish waters. A vertical size distribution of coccohthophorids at 

 equatorial stations has been reported." Small forms were abundant in the 

 upper 50 meters. Near surface temperatures are also a probable factor in 

 distribution. It is thought that variety, large size, and abundance of Eocene 

 coccolithophorids indicate "warmer seas. "•''•'' 



The life cycle of coccolithophorids has recently been shown to be more 

 complex than previously thought.'** A motile stage and a cyst stage have been 

 experimentally demonstrated for Coccolithus pelagiciis}^ 



From these data, shape, size, and encystment seem to be adaptations similar 

 to those in the closely related siliceous Chrysomonadina. Coccolilh formation, 

 shape, their even spacing in the membrane, and spinelike processes arising from 

 some coccoliths, are all adaptive devices to aid flotation. Abnormal amounts 

 of calcite in some Tertiary coccoliths are thought to reflect calcium carbonate 

 rich waters and not a diagenetic effect.''^ Conceivably, this abnormal deposi- 

 tion may have served to aid buoyancy or to adjust specific gravity. 



One can confidently transfer the general interpretation given to Tertiary 

 coccolithophorids. 



The silicoflagellates have a siliceous skeleton which is covered by a delicate 

 layer of cytoplasm containing chromatophores. This occurs in early develop 

 ment when the skeleton is internal, whereas in the adult individual it is ex- 

 ternal.-''^ The skeleton ranging in size from 10 to 150 fx is essentially a "lattice- 

 work case of hollow siliceous bars."^" Dislephanus ( = DictyocIia) speculum 

 with 6 radial spines may be taken as an example of the group. In most silico- 

 flageUates, the spines give the skeleton a stellate appearance. There may also 

 be accessory and basal spines. The basal body ring may be from 3 to 10-sided 

 with as many radial spines. Radial spines issue from the point of intersection 

 of any 2 sides. The basal body ring of .some fossil forms like Mesocena and 

 Corbisema^^ is 3-sided with a small spine at each angle. Others, like Dictyocha 

 crux are 4-sided and have longer spines. D. speculum is 6-sided, and D. 

 flcfonaria is 8-sided .'^^ 



The siliceous skeleton is most often a complex of 2 rings or polygons joined 

 by a series of rods."* Dictyocha speculum is a good example of this construc- 

 tion. The basal body ring of Mesocena forms an ellipse, and in Corbisema, it 

 forms a triangle. 



Silicoflagellates are exclusively marine plankton'^'' and are found in colder 

 seas. Frequently they occur associated with diatoms and radiolarians in 

 ancient and modern sediments.^^ Although they are not uncommon in food 



I 



