THE PLANKTON OF EASTERN NOVA SCOTIA WATERS 



5 



SESSIONAL PAPER No. 22a 



GYMNODiNiUM. — Bergh. 



A form (Plate I., fig. 9) was observed on one occasion in July, 1902, which is 

 possibly referable to G. gracile Bergh. It is bright pink in colour and measures 

 125/A in its long diameter. In form it recalls G. fusus Schutt. — No. 2, Plate XXV., 

 fig. 81. 



PERIDINIID^. 

 DiNOPHYSis. — Ehrh, 



This genus is at once recognized by the compression from side to side and the 

 far anterior position of the transverse furrow. Two species are common at Canso and 

 at Malpeque; D. norvegica Clap, and Lach. (Plate L, fig. 10), the commonest form, 

 measures 65 !i in its long diameter, and can be distinguished by the coarse reticula- 

 tion of the shell, the green chromatophores and the curved posterior point. 



D. rotundata (Plate I., fig. 11), the next most frequent form, measures little 

 more than 50 /- in length, lacks chromatophores, possesses protoplasm of a very pale 

 pink hue, often much vacuolated, and has a shell decorated with very minute round 

 points. The anterior half of the shell projects considerably beyond the girdle, which 

 is notably not the case in D. norvegica. A third species of ovate outline with green 

 chromatophores, but smaller than either of the foregoing (35 — 45//), resembles D. 

 ovum, Schiitt, in form, but is not so large. 



PYROPHACUS. — stein, 



P. horologium Stein (Plate I., fig. 12) is distinguished by the fact that its two 

 valves are subequal and much flattened, so that it presents to the observer one or other 

 of its poles, being then distinguished by the broad transparent flanges overhanging the 

 transverse furrow. The chromatophores are yellowish green. It owes its specific 

 name to the watch-glass shape of its valves. These measure 72// in diameter. It 

 was common in the middle of July. 



PROTOCERATIUM. — Bergh. 



P. reticulatum Clap, and Lach, is a comparatively small form which no doubt f re • 

 quently eludes observation. It is marked by the coarse reticulation of the shell (Plate 

 I., fig. 13), which is divided off into angular areas bounded by ridges and pro"\#ied witli 

 a central pore, also by the deep diatom-brown of its chromatophores. It occurred at 

 Canso in July and August, the specimens measuring 46 // in the longest diameter. 



GONYAULAx. — Stein. 



G. spinifera Clap, and Lach. resembles the foregoing in its colouring, but has a 

 -^characteristic tubular prolongation of its anterior pole and carries spines on the post- 

 erior pole at the sides of the well-marked longitudinal furrow (Plate I., fig 14). The 

 transverse furrow is markedly spiral. The long diameter- is SO/j. . It was observed in 

 one gathering from Grand river, Malpeque in 1903. 



PERIDINIUM. — Ehrl. 



To this gemus there belong several species which are often most abundant in the 

 plankton, and constitute a very important element of the food of those animals which 

 are dependent on such microscopic nourishment. Four species were recognized at 

 Canso, not necessarily occurring at the same time, but frequently overlapping in their 

 maximum periods. Three of these have the angular outline which is characteristic of 



