14 MARINE AND FISHERIES 



5 GEORGE v., A. 1915 



of the intervening spaces also differ at different seasons of the year. Finally 

 sporangial frustules also differ considerably from the ordinary ones, the valves 

 being provided with short branched processes, and forms of this character have, 

 as in the case of Didadia, been constituted into different genera, though they are 

 now believed to be auxospores of the genus Chaetoceros. 



The genus Chaetoceros embraces a considerable number of species, but these 

 have as yet been very imperfectly differentiated, and much confusion exists as to 

 their identity and synonymy. In the descriptions which follow, and in Plates 

 to which these refer, only such forms are included as the writer has himself ob- 

 served in the coastal waters of New Brunswick and mainly from the Bay of Fundy, 

 with suggestions as to their probable indentity with those found elsewhere. 



Plate I. Fig. I. Chaetoceros decipiens. — Cleve. 



This is perhaps the most common of the species found about Passamaquoddy 

 Bay, as Prof. Ramsay Wright reports it to be at Canso, Nova Scotia. The frustules 

 are quadrangular, with concave faces, producing between adjoining cells a vacant 

 space which is elliptical or approximately hexagonal in outline, while the lateral 

 bristles arise from the points of contact between the frustules, and for short 

 distances may be confluent. The bristles are four in number at each point, but 

 of these only two belong to each frustule. They are filiform and of only moderate 

 length, perhaps three or four times that of the diameter of the frustule. The 

 terminal bristles are shorter, bearing transverse striae, and, though divergent at 

 a considerable angle, are more nearly parallel than the lateral ones with the 

 axis of the chain. 



Plate I. Fig 2. Chaetoceros decipiens. — Cleve, (Var). 



This form differs from the preceding in the much closer approximation of 

 the frustules, together with the very slight concavity of their opposed surfaces, the 

 intervening space being narrowly linear. Two smooth and filiform late/al awns arise 

 on each side of the junction lines, diverging at an angle of about 30°, and, by 

 intersection with their fellows, produce the appearance of lattice-work. The 

 terminal awns have not been observed. The form is believed to be a variety of 

 Ch. decipiens, Cleve, the shape of whose cells, and therefore of the interval 

 separating the latter, are known to vary with the seasons and other conditions. 



Plate I. Fig. 3. Chaetoceros. 



This form resembles that of Ch. decipiens, Cleve, in the general form of the 

 frustules and in the arrangement of the horns or bristles, but the terminal awns 

 are clavate and symmetrically curved to enclose a space forming about one half 

 of a broad ellipse. The chromatophores are condensed in the centre of each 

 frustule. In the clavate form of its terminal awns it resembles what some authors 

 have described and figured under the name of Ch. didadia, but these are now 

 usually regarded as varieties of Ch. decipiens. 



