THE PLANKTON DIATOMS OF THE BAY OF FUNDY 13 



SESSIONAL PAPER No. 39b 



ring at Canso, N.S. are given, and these have been of service in the study of the 

 New Brunswick forms. 



In the following account of the species entering into the composition of the 

 Plankton those which may be regarded as especially characteristic of the latter, 

 exhibiting the most marked adaptations to a life of flotation, will be first consider- 

 ed, to be followed by those which, though less marked in this respect, are neverthe- 

 less of general or frequent occurrence. 



Prof. W. A. Herdman, F.R.S. of Liverpool University, who has been in charge 

 of special plankton investigations around the Isle of Man, gives six genera as those 

 which are especially characteristic of the plankton flora of that region, and it is 

 interesting to note that, with one possible exception (Lauderia) all of these occur 

 and in most instances are abundant in the Bay of Fundy and adjacent waters. 

 These genera are Chaetoceros, Rhizosolenia, Biddulphia, Coscinodiscus, Thalassiosira 

 and Lauderia, to which may be added Skeletonema, Bacteriastrum and Asterionella. 



Descriptions of Genera. - 



Chaetoceros. This genus is probably the most remarkable one among the 

 Plankton Diatoms, and exhibits the widest divergence from the ordinary type 

 of these plants, leading some authois to doubt whether they should leally be con- 

 sidered as Diatoms at all. Their most noticeable feature is that of their being pro- 

 vided with spines, awns, or bristles, which, though usually very thin, greatly exceed 

 in length the diameter of the frustule to which they are attached, and sometimes 

 exceed the latter fifty times or more. The f rustules are usually arranged in chains , 

 embracing a considerable number of individuals, which may be united either by 

 a band or cingulum, or by the interlocking of the horns. These latter vary in 

 number from two to four, and most of them are arranged laterally or at right 

 angles to the chain, being sometimes attached to or proceeding from the usually 

 convex valves of the frustules above and below, so as to interlock and thus add 

 strength to the chain, or in some instances from the cingulum, or from both. In 

 addition to the lateral bristles there are often terminal ones as well, usually two in 

 number which are either longer or shorter than the others, and may also differ 

 from them in other respects as well. 



Though usually single, the spines may sometimes bifurcate near their point of 

 origin, and while commonly smooth throughout, are often spinous or serrated or 

 presenttheappearance of bearing imbricated scales. Occasionally they seem to have 

 a spiral twist, like a screw. In the case of the terminal awns, though usually bristle- 

 like, they are also sometimes clavate or somewhat spatulate, suggesting comparison 

 with the antennae of lepidopterous insects. Some awns are stout and rigid, others 

 fine or hair-like and flexible. Their length seems to be connected with their age, 

 the terminal awns being also often much longer than the lateral ones. The angle 

 of divergence of the awns and the disposition of the chromatophores have both 

 been regarded as of diagnostic importance, but the observations of the writer 

 hardly accord with this view, different frustules of the same chain exhibiting 

 considerable diversity in both these respects. The shape of the cells and therefore 



