A new form is described in the polytypic species Clio pyramidata LINNAEUS, 1767. This new forma excisa was found at 57°31'S 02°56'W and it is related to the forms convexa (BOAS, 1886) and sulcata (PFEFFER, 1879). The shape of the shell of the new form excisa shows a great resemblance to the shape of the shell of these two forms and also a resemblance is present to the shape of the shell of the form martensii (PFEFFER, 1880). This resemblance, however, may indicate a relationship as well as a parallel development. The new forma and the form martensii live in the same area, so that the chemo-physical characteristics of the water may have caused a parallel development. As indicated in a previous paper, the polytypic species Clio pyramidata consists of several forms which can be divided into two groups, one with the form antarctica. (DALL, 1908) as the most sourthern form and the other one with the form sulcata as the most southern one. As the new form shows a relation in shape with the forms sulcata, convexa and martensii and not with the form antarctica, it seems correct to suppose that the new form excisa belongs to the same group in the polytypic species in which the forms sulcata and convexa are placed. In the same sample some specimens of the forma sulcata were present, and among these, two were in a resting-stage and one in an intermediatestage. A real resting-stage in the forma sulcata was never found before.

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Journal Beaufortia
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van der Spoel, S. (1963). A new forma of the species Clio pyramidata Linnaeus, 1767 and a new resting-stage of Clio pyramidata Linnaeus, 1767 forma sulcata (Pfeffer, 1879) (Gastropoda, Pteropoda). Beaufortia, 10(114), 19–28.