The variation in an assemblage of the Caninia Cornucopiae plexus from the Middle Viséan>

Summary A Caninia cornucopiae assemblage of C 1 age and one S 2 D 1 are both shown to consist of a dominated and several subsidary forms. The dominant form of the newer assemblage, which is described as C. lanceolata sp. nov., shows a definite structural advance on that of the older assemblage, the change being considered to be palin-genetic. Lengthy conocylindrical forms are found in both assemblages; their distribution is discussed and they are considered to be forms successfully adapted to an initially adverse environment by a change in relative growth-rate.