6 



MARiyE AND FISHEIUEi^ 



6-7 EDWARD VII., A. 1907 



most of the species, while the fourth is oval in contour. The three former, however, 

 differ in dimensions and in colour. P. divergens v. reniforme Ehrb. (according to 

 Jorgensen, No. 3, p. S6=P. depressum Bailey) is the largest (120ja in transverse 

 diameter) and has protoplasm of pinkish hue (Plate I., fig. 15, a. & b.). P. lenticulare 

 Ehrb. (Plate I., fig. 16), is greenish, and measures only 80;^- across, while P. pellucidum 

 fig. 17) is only half as wide, more pyriform, and quite colourless. At the beginning of 

 August, 1902, a variety of P. divergens made its appearance, in which the pink colour 

 was more intense, the reniform outline, when observed from one of the poles (fig. 15 c.) 

 more marked, and the vertical height from pole to pole less. P, ovatum (Pouchet) Schiitt 

 (fig. 18) shares the pink hue of P. divergens, but is oval in outline except for the short 

 tube of the apical pole. Its transverse diameter is 75//. and its vertical 55/>'-. The 

 venrral fissure is bounded by two sharp teeth. 



Diplosalis lenticula Bergh, was observed along with the foregoing, with which it 

 may easily be confused on account of its oval outline, but it differs from it in posses- 

 sing only five pre-equatorial plates instead of seven, and in the fact that the transverse 

 furrow has a strictly equatorial and not slightly spiral course. Its dimensions are 

 rather smaller. 



CERATIUM. — Schranh. 



This genus, like Peridinium, furnishes a very large part of thje floating food- 

 material of the ocean. It differs from it in having the tendency to develop flotation 

 organs either in the form of three horns (one apical, two antapical), or by the acquisi- 

 tion of an exceedingly long and slender form like some of the plankton diatoms. The 

 plates of the apical pole are fewer in number, there being only three pre-equatorial 

 plates. 



The commonest species at Canso is the widely-distributed C. tripos Nitsch, and 

 the variety of this very variable species which is most abundant is G. tripos macroceras 

 (forma intermedia) of Jorgensen. It will be seen that my sketches (fig. 19) resemble 

 his figure (ISTo. 3, Plate I., fig. 10) very closely. Another form in which the horns are 

 much longer in proportion to the width of the body was commoner, earlier in the year, 

 and is perhaps the form scoticum ' of Schiitt, while isolated examples of a form with 

 the antapical horns very slightly curved tow^ards the apical pole approach the variety 

 ' arcticum! 



C. fusus (fig. 20) seems less variable than the foregoing. The right antapical horn 

 is more or less suppressed, and the whole cell attains a length of over 1 mm. 



^ GYMNASTER. — Schiltt. 



One or two examples of the singular little form G. p&ntasterias Ehrb. (fig. 21 a. & 

 b.) were met with in July. The body is oval, 44/^- in long diameter, and is distinguished 

 by the presence of two intracellular skeletal plates of resistant siliceous material. After 

 boiling with nitric acid the delicate form of these plates (No. 2, fig. 216) becomes 

 more evident. This form is frequently regarded as one of the Silicoflagellata (p. 9). 



DIATOMAGE^. 



Of this group a very large number of marine forms are known, some of them ad- 

 mirably adapted as Schiitt has pointed out (Pflanzenleben der Hochsee) for a float- 

 ing life; others on the other hand confined to a littoral life by the absence of such 

 provisions. The adaptation for floating is generally achieved by a reduction in 

 the amount of silica in the valves of the shell, and in addition by the flattening of the 

 whole cell into a disc-like form or its elongation into a more or less needle-like shape. 

 Goscinodiscus and Rhizosolenia exhibit the two extremes of these modifications, 

 and both genera were frequently represented in the tow-nettings at Canso. Of the 



