OBSERVATIONS AND REMARKS ON THE MORPHOLOGY AND TAXONOMY OF THE DIATOM GENERA GYROSIGMA HASSALL AND PLEUROSIGMA W. SMITH III. GYROSIGMA STERRENBURGII SP. NOV., AND PLEUROSIGMA AMARA SP. NOV.

Abstract

Specimens of Gyrosigma and Pleurosigma taxa from four New Zealand sites have been studied. Studies and comparisons have been made of New Zealand and European populations which conform to G. balticum (Ehrenb.) Rabenh. as well as European populations of P. elongatum W. Smith, identified by reference to the type. The New Zealand taxa are distinguished by marked specific differences, particularly in apical structure. Structural instability of the external central raphe fissures is also demonstrated.

Two new taxa, Gyrosigma sterrenburgii and Pleurosigma amara, are described and discussed.