56 



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



and right posterior sulcal lists 2 girdle widths wide. 

 They do not extend to posterior end of ventral area, but 

 end about halfway down posterior sulcal plate (fig. 66G). 

 Sulcal lists quite evident in lateral view (fig. 66D). 

 Right sulcal list is attached to po6; the left is in two 

 parts, attached posteriorly to p and anteriorly to pol. 

 The portion of the ventral area which is free of lists 

 (the posterior part) is limited to the region bordered by 

 the antapical plate. Left list usually without structural 

 differentiation, but the right has short ribs or reticula- 

 tions at its base. Antapical spine thick, solid, irregu- 

 larly furrowed, about 2.5 girdle widths long. 



Historical . This species was first reported by 

 Kofoid (1911b), who identified his material with Gonyau - 

 lax j oUiffei Murray and Whitting (1899) and assigned it 

 to the new genus Spiraulax . Since, in our opinion, Mur- 

 ray and Whitting's specimens do not belong to Spiraulax 

 (see p. 52), we are here assigning a new name to Ko- 

 foid's species, Spiraulax kofoidii new name. 



Distribution . The references of Schroder (1900) 

 and Karsten (1907) to Gonyaulax j olliffei Murray and 

 Whitting for the Mediterranean and Indian oceans, re- 

 spectively, should not be accepted, since the figures of 

 Murray and Whitting have not yet been positively identi- 

 fied. The records of Spiraxilax j olliffei Kofoid of Pavil- 

 lard (1931) and of Matzenauer (1933), however, probably 

 refer to the present species. Pavillard found it in the 

 Atlantic and Mediterranean; Matzenauer in the Indian 

 Ocean. Forti's (1922) records for the Mediterranean 

 are not substantiated by drawings as his drawings are 

 copies. 



In the Carnegie collections Spiraulax kofoidii was 

 found at most of the tropical stations. It occurred at 

 80 stations: 12 in the Atlantic and 68 in the Pacific. 

 There are 162 records of occurrence, with 119 rare, 39 

 occasional, and 4 common. The species was found less 

 commonly with increase in depth, with 66 records for 

 the siirface, 51 for 50 meters, and 45 for 100 meters. 

 There are 39 pump records and 123 net records. The 

 species was found in both hemispheres and in all months 

 of the year, except June and July. 



The species Is widely distributed over tropical and 

 subtropical stations, although the records are not contin- 

 uous. In the Atlantic it occurred in the Gulf Stream as 

 far north as 38° north (station 1, surface temperature 

 24° C). Otherwise it was not found north of 24° north in 

 that ocean (station 19, surface temperature 27° C). In 

 the Pacific it was found only to 26° north in the west 

 (station 110, surface temperature 24° C) but to 37° 

 north in the east (station 130, off California, surface 

 temperature 16°2 C). In the South Pacific it did not oc- 

 cur farther south than 35° south (station 62, surface 

 temperature 19° C). It was most abimdant north of 

 Easter Island and in the line of stations east and north 

 of the Samoan Islands. 



The surface temperatures at the stations where it 

 occurred at any depth varied from 19° to 29°.3 C, ex- 

 cept for the one record off California (station 130), 

 where the temperature was 16°2. The hydrographlc 

 conditions in situ were as follows: temperature, 13°.l 

 to 29°2 C; saUnity, 33.4 to 37.1 o/oo; pH, 7.80 to 8.47; 

 phosphate, 2 to 178 mg PO^/m'. 



The species is probably indigenous to the areas with 

 Rrater of low nutrient content as well as to richer tropi- 

 cal waters, as there are 59 records in water containing 

 less than 10 mg P04/m3. 



Family CERATIACEAE Lindemann 

 Diagnosis. See Lindemann, 1928, p. 91. 

 Genus CERATIUM Schrank 



Diagnosis . See Lindemann, 1928, p. 92. 



Remarks . Although the genus Ceratium is one of 

 the commonest and most widespread of the peridinlans 

 and is usually the first genus to be reported from ex- 

 pedition collections, its thecal morphology is still as 

 poorly known as that of the rarer genera. In order to 

 contribute something toward the knowledge of the mor- 

 phology of the genus and to endeavor to find something 

 which might throw light on the relationships of Cerati - 

 um to other genera, C. pavlllardii was selected for 

 study and subjected to a morphological analysis. 



That this analysis was not so successful as in the 

 case of the other genera is not discouraging. Sufficient 

 knowledge was gained to indicate that such studies with- 

 in this interesting genus may be quite helpful in solving 

 some of the systematic problems and in arriving at a 

 proper imderstanding of relationships. 



Ceratium arcticum was also dissected, but in this 

 species no trace of the ventral area had been preserved, 

 so that only the grosser features could be determined. 

 For this reason it is not reported here except as re- 

 ferred to under "Comparisons" under C. pavlllardii . 



Ceratium pavlllardii Jorgensen 

 (Figure 67) 



Ceratium pavlllardii Jorgensen, 1911a, p. 74, figs. 157A, 

 B, 158. Jorgensen, 1920, p. 92, fig. 83. 



Ceratium yultur Pavillard, 1905, p. 54, pi. 1, fig. 2. 



Ceratium tripos var. macroceras f . undulata Schroder, 

 1900, pi. 1, fig. 17m [not fig. 17K, L]. 



Diagnosis . Diameter (d) 78 (60-90) microns. Api- 

 cal horn more or less straight. Base of right antapical 

 horn extends laterally from body. Base of left antapical 

 horn bent abruptly anteriorly; sometimes there is a 

 short posterior extension before the turn. Otherwise no 

 posterior extension of antapicals. Antapical horns ex- 

 tend laterally to anteriorly. 



Plate pattern . First apical with long margin on 

 ventral area; fourth apical with very short margin on 

 area. 



Girdle plates four. The functional girdle probably 

 includes only the first three of these. First and fourth 

 girdle plates short, ventral; second and third long, dor- 

 sal. Suture gl/g2 in line with sutures prl/pr2 and 

 pol/po2. First and second plates regular in outline. 

 Third plate with distal end hammer-shaped (fig. 67D, F), 

 probably marking end of girdle proper, as girdle lists 

 end at this point. Fourth girdle plate peculiarly modi- 

 fied at Its distal end to form the concave roof of the 

 horn trough (fig. 67E, G). 



Fifth postcingular, which forms ventral half of 

 right antapical horn, is molded at its proximal end to 

 form the horn trough (fig. 67G). In chains this trough 

 encloses anterior part of apical horn of adjacent spec- 

 imen immediately posterior. It is found in all speci- 

 mens, since all specimens form at least temporary 

 chains at division. 



Ventral area composed of a numJser of extremely 



