British sea-weeds, London, Bell and Daldy, 1872, algae, Great Britain, marine algae, A collection of botanical illustrations showcasing various species of *Calothrix*, a genus of cyanobacteria known for their filamentous structures. The illustration is organized into several sections, each depicting different forms and characteristics of these organisms. Examples include *Calothrix luteola*, *Calothrix fasciculata*, and *Calothrix scopolorum*, alongside distinct variations like *Calothrix semiplana* and *Calothrix hydroides*. These illustrations highlight the diversity in morphology, with various shapes, sizes, and arrangements reflecting the unique attributes of each species within the genus. The series exemplifies the intricate details and systematic classification used in the study of algae and cyanobacteria.