PREFACEnarrowly circumscribed of necessity, one should perhaps be thankful that in the midst of the difficulties of this atomic age any progress has been made at all.It would be invidious, in a work which owes such a heavy debt to others, to select many names for special mention. An exception must, however, be made for Professor W. H. Lang, without whom the work would not have been done at all. And of the many contributors who are not my colleagues, I must record a special debt to

No abstract

Coccolith structure, mode of origin and arrangement on the cell surface have been investigated in two marine coccolithophorids, Coccolithus pelagicus (Wall.) Schiller and Cricosphaera carterae (Braarud et Fagerland) Braarud, by means of light microscopy and electron microscopy of whole mounts and sections. The presence of flagellar bases in Coccolithus pelagicus is also demonstrated in spite of the fact that the cells of this phase of the life-history are non-motile. In both organisms the coccoliths are shown to be accompanied by unmineralized scales, details of which are illustrated; in particular, each coccolith is attached to the margin of an unmineralized oval plate which completely covers the central ‘pore’ on the side towards the subtending cell. Scales and coccoliths arise within the cisternae of the single Golgi body in a manner closely resembling the origin of scales in species of Chrysochromulina. It is therefore suggested that the coccoliths of the two taxa investigated can be interpreted as modified (and calcined) scale rims.

The three new species to be described below are the first of a considerable series of related forms, recently isolated from marine plankton off the British coasts and possessing in common a number of rather unusual characters which make their classification difficult. They are all very small and extremely fragile unicellular flagellates, with the characteristic golden brown plastid colour and metabolic products found in the Chrysophyceae to which they undoubtedly belong. Within this group their placing is more difficult and it cannot even be adequately discussed until the whole range of new forms is available for comparison. The most that we can do on this occasion is to make some provisional generic comparisons in order to establish a system of nomenclature. Unfortunately, existing descriptions of relevant genera are both scanty and incomplete, a defect which is easily explained by the nature of the organisms and the need for special facilities for their adequate study.