18 



STUDIES IN THE MORPHOLOGY, TAXONOMY, AND ECOLOGY OF THE PERIDINIALES 



Peridinium depressum Bailey 

 (Figure 14) 



Peridinium depressum Bailey, 1855, pp. 12-13, pi. 



figs. 33, 34. Jorgensen, 1899, p. 36, tabs. 4, 18, 30, 

 44, 58, 72. Ostenfeld, 1900, p. 57, tabs. 2-7. Cleve, 

 1900b, p. 257. Jorgensen, 1901, p. 34. Gran, 1902, 

 pp. 186, 191-192. Jorgensen, 1905, p. 109. Van 

 Breeman, 1905, p. 43. Broch, 1906, pp. 151-157, 

 fig. 1. Paulsen, 1907, pp. 11, 15. 1908, pp. 39, 53, 

 fig. 67. Broch, 1908, p. 5. 1910, pp. 51-52, fig. 26. 

 Meunler, 1910, p. 27. Paulsen, 1913, pp. 276-279, 

 pi. 46. Mangin, 1913, pp. 158-160, 162-164,166- 

 169, 171, 177-178, 180, 187, 220-222, fig. 9, tabs. 

 1-3. Jorgensen, 1913, pp. 5-6. Forte, 1922, pp. 89, 

 188, 207. Lebour, 1925, p. 119, pi. 23, figs. a-f. 

 Dangeard, 1926, p. 322, fig. 10. Dangeard, 1927b, 

 p. 2, figs. lA-lC. Paulsen, 1930, pp. 55, 68. Pavil- 

 lard, 1931, pp. 55, 64-65, 111-112, 114-115, 121, 

 123, 125, 127, 129, 131, 133, 137, 157, 159, 161,165, 

 169, 173, 177, 183, 185, 191, pi. 2, figs. 6A-6E. 

 Gran, 1933, pp. 162, 180. 



? Peridinium divergens y renifqrme Ehrenberg, 1854, 

 p. 240. Meunier, 1910, p. 23, pi. 1, figs. 1-4. 



Ceratium divergens Claparede and Lachmann, 1861, p. 

 71, pi. 13, fig. 23. 



Peridinium divergens . Bergh, 1881, pp. 63, 67, 70, 73. 

 Bergh, 1882, pi. 15, fig. 45. ? Stein, 1883, pi. 11, 

 figs. 1, 2. Vanhoffen, 1897a, pp. 267-268, pi. 5, fig. 



1. Cleve, 1900a, figs. 15, 16. Meunier, 1910, pi. 2, 

 figs. 45, 46. Lebour, 1917, p. 186. Meunier, 1919, 

 pp. 12-14, pi. 15, figs. 1-5. 



Peridinium divergens vari^te, Pouchet, 1883, p. 40, pis. 



20, 21, fig. 23. 

 Peridinium divergens var. reniforme , Pouchet, 1883, p. 



40, pis. 20, 21, figs. 24-27. 

 not Peridinium divergens var. typus . Pouchet, 1883, p. 



38, pis. 20, 21, figs. 20, 21. Ostenfeld, 1899, p. 60, 



84, tabs. 1-8. 

 Peridinium divergens var., Schutt, 1895, pi. 13, figs. 



43(22), 43(24). Meunier, 1910, pi. 1 (bis), figs. 1, 



2, 7, 8. 



Peridinium divergens var. depressa . Aurivillius, 1898, 



p. 55. Ostenfeld, 1899, pp. 60, 70, 86, tabs. 1-8. 

 Peridinium elegans Cleve, 1900a, in part, pi. 7, fig. 16. 

 Peridinium depressa , Ostenfeld, 1900, tab. 1. 

 Peridinium divergens var. depressum . Karsten, 1907, 



p. 466. 

 Peridinium kofoidii Faure-Fremiet, 1908, pp. 224-226, 



fig. 11, pi. 16, fig. 12. Mangin, 1913, p. 222. 

 Peridinium marinimi Lindemann, 1925, pp. 98-99, figs. 



7-11. 

 Peridinium marinum var. travectum Lindemann, 1925, 



p. 99, fig. 12. 



Dimensions . Length of body (i) 187 (114-228) mi- 

 crons; diameter (d) 137 (108-160) microns. Width of 

 girdle, about 7 microns. Eighty specimens were meas- 

 ured. 



Shape . Length of body, exclusive of antapical horns, 

 normally equal to diameter of body at girdle as shown 

 by the h/d ratio, which is 1.00 (0.77-1.18). The angle a 

 is 95° (78°-105°). The a/d ratio is 0.39 (0.21-0.65); that 

 is, length of right antapical horn normally about 0.4 

 times width of body at girdle. The b/a ratio is 0.14 

 (0.08-0.27); that is, right antapical horn normally about 

 0.14 times as thick as long. 



Cell body very asymmetrical. Roughly, the mid- 

 body is a lenticular mass depressed along an anteroven- 

 tral-posterodorsal axis running at an angle of about 55° 

 to plane of girdle. Epitheca tapers abruptly on lateral 

 and dorsal faces, but gradually on ventral side, into an 

 apical horn which extends along an axis which lies at an 



angle of about 65° to the axis of depression of mid-body. 

 Hypotheca terminates in two antapical horns which are 

 pointed and more slender than the apical horn. Right 

 antapical horn may lie parallel to axis of apical horn, 

 but usually diverges somewhat laterally to the right. 

 The left one is shorter than the right and diverges from 

 it laterally and ventrally. The girdle leaves the sulcus 

 on the left side of the body, curving forward to a point 

 about halfway to the left side of body, where it begins to 

 turn gradually backward. This backward curvature is 

 continued entirely around the body, so that the distal 

 end of the girdle terminates on the right side of the sul- 

 cus from 1.5 to 2.5 girdle widths behind the proximal 

 end. This does not represent the maximum displace- 

 ment of the girdle, however, which occurs between the 

 distal end and the front of the curvature to the left of the 

 sulcus. This displacement is about 3 girdle widths. 

 The displacement of the girdle can be seen only when 

 the specimen is viewed ventrally. When the specimen 

 is allowed to come to rest in a drop of water on its pos- 

 terodorsal surface, a position commonly represented in 

 published figures, no displacement of the girdle is evi- 

 dent (fig. 14A). Girdle not concave. Body reniform in 

 apical or antapical view, with the indentation at sulcus. 

 Theg/d ratio, about 0.75. Ventral area narrow, with 

 more or less parallel sides, 2.0 to 2.5 girdle widths 

 wide. Sulcus proper deeply embedded, extending to ant- 

 apex. Anteriorly the ventral area extends very slightly 

 beyond proximal end of girdle. 



Plate pattern . The first symmetrical and first a- 

 symmetrical patterns occurred in the proportion of a- 

 bout 4 to 1. The frequency distribution of the two pat- 

 terns is shown in figure 10. 



The apical horn terminates in a more or less trun- 

 cated apex, about 8 microns in diameter. This region is 

 much more complex than was at first supposed. It is not 

 formed simply by the apical ends of the four apical 

 plates. In fact, the first apical plate ("rhomboid plate" 

 of Kofoid or "Rautenplatte" of Butschli) does not extend 

 entirely to the apex. The first apical, or rhomboid, 

 plate terminates about 9 microns below the apex, where 

 it borders on a narrow ventral apical platelet (v. a. p., 

 fig. 15) which extends to the apex. This platelet is al- 

 most rectangular in outline, about 9 microns long and 

 slightly more than 2 microns wide. Its posterior end is 

 convex, where it fits into an equivalent concavity in the 

 anterior end of the rhomboid plate. This convexity may 

 be slight or, in some cases, extreme. Since the rhom- 

 boid plate does not reach the apex, it is not an apical 

 plate, strictly speaking. It seems desirable, however, 

 to retain the term "first apical" for this plate because 

 the ventral apical platelet is extremely small and per- 

 haps not equivalent to the other apicals. The possibili- 

 ty of the homology of this platelet with the major plates 

 of the other genera, however, should not be overlooked. 



The exterior of the apex is formed by the ventral 

 apical platelet on the ventral side and the anterior ends 

 of the second, third, and fourth apical plates on the left, 

 dorsal, and right sides, respectively. The joining of 

 these plates is strengthened interiorly by a pore plate- 

 let, sleevelike in form, around which the ends of the ex- 

 terior plates fit snugly. This apical pore platelet (a. p. p., 

 fig. 15) is about 5 microns in diameter and 3 microns 

 long. Its walls are about 1.5 microns thick, so that the 

 apical pore, representing the bore of this sleeve, is a- 

 bout 2 microns in diameter. 



The girdle is composed of four plates (lg-4g, fig. 



