582 



Annals of the Smith African Museum. 



Crass, fil. ram. apical., 9-12//,; crass, trich., 6-9 /a; lat. heterocyst., 

 9-12 /jl; crass, vag. ad bas., usque 5 fx. 

 Sample 42. 

 The species of Bichothrix and their relation to those of the genus 



Fig. 38. — Bichothrix fusca, n. sp. A. Entire plant, showing 1 the habit and 

 the general character of the filaments. B. Base, and C, apex of a 

 single filament. A, x 195 ; B and C, x 37o. 



Calothrix are so imperfectly known that I must confess to some 

 hesitation in describing the form in sample 42 as a new species. I 

 have, however, been unable to convince myself of the correspondence 

 of the latter with any of the forms hitherto described. D. fusca 

 belongs to that group of species in which the sheaths gradually taper 



