FAMILY PERIDINIACEAE 



27 



tern except that there were two, instead of three, inter- 

 calaries. In one of the three specimens examined, the 

 suture between the two intercalaries was so displaced 

 to the right of the median body line that it appeared to be 

 the normal suture between 2a and 3a and that the left 

 plate represented a fusion of la and 2a. In the other 

 specimens, however, as in the two-intercalary form of 

 P. depressum . the suture between the two intercalaries 

 was medially located and thus indicated a more funda- 

 mental change in the organization of the plate pattern. 



Comparisons . This form occupies the same posi- 

 tion relative to P. oceanicum that P. depressum f. bis- 

 intercalatum does to P. depressum . It is distinguished 

 from P. oceanicum only by the presence of two instead 

 of three anterior intercalary plates. 



Occurrence. This form appeared at three stations, 

 all in the Atlantic: in the North Atlantic West Wind Drift 

 (station 2) at the surface, on the Grand Banks of New- 

 foundland (station 13) at 50 meters, and in the Caribbean 

 Sea (station 31) at 100 meters. Its relative abundance at 

 the last station was occasional; at the other two stations, 

 rare. The ranges of hydrographic conditions in which it 

 was found were as follows: temperature, -l!64 to 

 22!56 C; salinity, 33.4 to 36.5 o/oo; pH, 7.86 to 8.23; 

 phosphate, 28 to 58 mg P04/m3. 



It is obvious from the above data that the aberrant 

 pattern exhibited by forma bisintercalares does not ap- 

 pear under any limited set of hydrographic conditions. 

 Thus, it is probable that the causes of the development 

 of this pattern are genetic rather than environmental. 

 Type locality: Carnegie station 13. 



Peridinium oceanicum forma tricornutum n.f. 

 (Figure 36) 



Dimensions. Length of body {V) 203 microns. Di- 

 ameter (d) 120 microns. Width of girdle about 5 microns 

 One specimen was measured. 



Shape . The general dimensional relationships are 

 similar to those in P. oceanicum . The h/d ratio is 1.21. 

 The angle a is 110°. The a/d ratio is 0.48. The b/a 

 ratio is 0.13. The left side of the mid-body is swollen 

 into a roughly hemispherical protuburance involving 

 both the epitheca and the hypotheca. The proximal end 

 of the girdle has an unusual displacement anteriorly, o- 

 ver four girdle widths. 



Plate pattern . The epithecal tabulation is of the first 

 symmetrical pattern. The x-ratio is +1.43. The hypo- 

 thecal side of the hemispherical protuberance is drawn 

 out into a hollow horn with attenuated tip. This horn is 

 composed of one plate representing an additional or pos- 

 terior intercalary plate, inserted between the first, sec- 

 ond, and third postcingular and the first antapical plates. 



Comparisons . Whether this form represents a pre- 

 mature development of the theca during division, or 

 whether it is an expression of a definite tendency in the 

 thecal variation, cannot be determined. It is unique in 

 that it is the only specimen observed in which any vari- 

 ation occurs in the hypotheca. 



Remarks . Names were assigned with hesitancy to 

 such aberrant forms as f. tricornutum and f. spiniferum 

 because of the realization that these forms may repre- 

 sent pathological conditions. Since there were no defi- 

 nite indications of the pathological nature of the speci- 

 mens examined, however, and since some species of the 

 Peridlnlales, e.g., Ceratium hlrundinella . normally 



have multiple horns, it was decided to assign names to 

 these forms, thus expressing the possibility of their 

 representing incipient species. 



Distribution . The specimen was collected in Au- 

 gust 1928 in the 50-meter sample at station 13 on the 

 Grand Banks of Newfoundland, where so many variants 

 of P. depressum and P. oceanicum were found. The hy- 

 drographic conditions were as follows: temperature, 

 -1°.64 C; salinity, 33.4 o/oo; pH, 7.86; phosphate, 60 mg 

 P04/m3. Type locality: Carnegie station 13. 



Artificial Key to the Units of the Section Oceanica 

 Treated in this Report 



A. The h/d ratio less than 1.20; or if greater, the angle 

 a less than 105° B 



A. The h/d ratio more than 1.20 and the angle a great- 

 er than 105° : H 



B. The angle a. 105° or less C 



B. The angle a greater than 105° F 



C. Epitheca with 2 intercalary plates 



P. depressum f.bisintercalatum n.f. 



C. Epitheca with 3 intercalary plates D 



D. Epitheca composed of 17 major plates 



P. depressum f. multitabulatum n.f. 



D. Epitheca composed of 14 major plates E 



E. Antapical horns cuneate; b/a ratio greater than 0.23; 

 epithecal pattern usually second symmetrical . . . 

 P. claudicanoides n.sp. 



E. Without this combination of characters 



P. depressum Bailey 



F. The a/d ratio less than 0.30 



P. depressum var. parallelum Broch 



F. The a/d ratio more than 0.30 G 



G. Lateral contours of body convex 



P. depressum var. convexius n.var. 



G. Lateral contours of body straight or slightly convex . 

 P. depressum var. rectius n.var. 



H. Epitheca with 2 intercalary plates 



P. oceanicum f. bisintercalares n.f. 



H. Epitheca with 3 intercalary plates I 



I. Fourth apical plate bearing a prominent spine . . . 



P. oceanicum f. spiniferum n.f. 



I. Fourth apical plate not bearing a prominent spine . 



J 

 J. Hypotheca with an intercalary plate bearing a horn 



P. oceanicum f. tricornutum n.f. 



J. Hypotheca without such a plate K 



K. Total length (j.) less than 210 microns 



P. oceanicum var. tenellum n.var. 



K. Total length (1) more than 210 microns 



P. oceanicum VanhOffen 



Peridinium crassipes Kofoid 

 (Figure 37) 



Peridinium crassipes Kofoid, 1907a, pp. 309-310, pi. 31, 

 figs. 46, 47. Paulsen, 1907, p. 17, fig. 24. Paulsen, 

 1908, p. 58, fig. 73. Broch, 1908, p. 5. Broch, 1910b, 

 p. 52, fig. 27. Okamura, 1912, p. 18, pi. 4, figs. 63a- 

 c. Lindemann, 1924, p. 230, pi. 4, figs. 80-86. Pe- 

 ters, 1928, p. 42, figs, lla-h. Matzenauer, 1933, p. 

 467, fig. 50. Bohm, 1936, p. 41, fig. 16c. 



Dimensions. Length of body (1) 105 (88-120) mi- 

 crons. Width of body (d) HI (90-130) microns. Width 

 (g) 80 (65-94) microns. Width of girdle about 6 microns. 



