CERATIUM SPECIES OF CARNEGIE COLLECTION 



19 



but is found at depths below the surface in a great many 

 cases. The table of frequencies (table 7), however, 

 shows that it was found most frequently at the surface. 

 This is particularly true of the records of "common" 

 and "abundant." 



The ranges of environmental conditions in situ were 

 as follows: temperature, 6.°6 to 29.°4 C; salinity, 33.1 to 

 37.0 per mille; pH, 7.63 to 3.47; phosphate, 3 to 233 mg 

 P04/m3. 



7. Ceratium belone Cleve 

 Figure 8, chart 7, appendix table 7 



This is a rare, intolerant tropical species confined 

 to water of high temperature. Peters (1934) found the 

 species in the South Atlantic not beyond 30° south. Niel- 

 sen (1934) found it in the Pacific scattered over the en- 

 tire region of the South Equatorial Current. 



In the Carnegie collection C. belone was foxmd at 

 twenty-six stations; two in the Atlantic and twenty-four 

 in the Pacific. The Atlantic records were in the middle 

 North Atlantic where the surface temperatures were 

 about 24° C (station lb) and 27.°0 C (station 18). The 

 most northern of these was at 38° north latitude. 



In the Pacific C. belone was found at one station off 

 Peru, at eleven stations around and north of Easter Is- 

 land, at seven stations east and north of Samoa, at one 

 station in the North Equatorial Current, and at three 

 stations in the central North Pacific (chart 7). Its lati- 

 tudinal limits were 33f 5 north and 32.°0 south, which is 

 a rather limited distribution for a species of Ceratium. 

 It is a curious and unexplainable fact that the species 

 was not found west of 179° west longitude. The surface 

 temperatures at the Pacific record stations varied from 

 20.° 4 to 29.°4 C. K must, therefore, be considered a 

 stenothermal species. Although it always occurred in 

 water of high temperature, it was seldom found in water 

 ef extremely low phosphate content. Only six of the fifty- 

 one records of occurrence were from water containing 

 less than 10 mg P04/m3. 



The ranges of environmental conditions in situ were: 

 temperature, 16.°0 to 29.°4 C; salinity, 34.1 to 37.0 per 

 mllle; pH, 8.11 to 8.47; phosphate, 5 to 48 mg P04/m3. 



Nielsen's (1934) classification of C. belone asasur- 

 face species is substantiated by the Carnegie data (table 

 8), although there were two records of "occasional" at 

 100 meters. The total percentages, however, show a 

 much more frequent occurrence at the surface than at the 

 lower levels. 



The occurrence of C. belone is sporadic. Unlike 

 some of the rarer tropical species, when it does occur, 

 it is sometimes foimd in considerable numbers. Peters 

 (1934) found this to be true in the South Atlantic. Like- 

 wise in the Carnegie collection there were several rec- 

 ords of "occasional." The total number of records was 

 fifty-one, of which forty-four were rare and seven were 

 occasional. 



Variation. --Ceratium belone is rather constant in 

 shape and size, except for the divergence of the antapi- 

 cal horns and the length of the apical horn. There is an 

 extreme variation in the total length of the specimens 

 (from 335 to 910 microns), but this difference is owing 

 entirely to the difference in the length of the apical horn. 

 The length of the hypotheca is constant. In only one 

 specimen (fig. 8H) was this elongate. The diameter, d, 

 varied from 20 to 30 microns. 



Table 8. 



Records of occurrence of C. belone Cleve 

 at three levels 



A=Nimiber of records. B=Per cent of total number of 

 samples collected at that depth. 



8. Ceratiimi incisum (Karsten) JSrgensen 

 Figure 9, chart 8, appendix table 8 



This is a rare, strictly tropical species with limited 

 distribution. Peters (1934) found it at only four stations 

 in the South Atlantic, and Nielsen (1934) found it at scat- 

 tered stations in the South Equatorial Current of the Pa- 

 cific. In the Carnegie collection it occurred at twenty- 

 seven stations- -two in the Atlantic and twenty-five in the 

 Pacific. There were thirty records of occurrence, all 

 rare. Twenty-two of these were from net samples and 

 eight were from pump samples. 



Of the two Atlantic stations, one was in the open At- 

 lantic at latitude 36.° 5 north, longitude 46.° 5 west (station 

 16); the other was in the Caribbean Sea. M the Pacific 

 the stations were scattered: one off Ecuador, six north 

 of Easter Island at about latitude 10° south, twelve be- 

 tween Samoa and Guam, four in the central crossing of 

 the equatorial regions, and two north of Hawaii. It was 

 very restricted in its latitudinal distribution and was ab- 

 sent from the southeastern Pacific region except at one 

 station off Ecuador. Its latitudinal limits in the Pacific 

 were 29° north and 15° south. In the Atlantic it occurred 

 to 36.°5 north. 



Ceratium incisum is a stenothermal form similar to 

 C. belone. The surface temperatures at stations at which 

 it occurred in the Atlantic were 25.°9 and 28.°5 C. In the 

 Pacific the range was 24.°6 to 29.°5 C. The ranges of en- 

 vironmental conditions in situ were: temperature, 14.°2 

 to 29.°3 C; salinity, 33.7 to 36.3 per mille; pH, 7.87 to 

 8.39; phosphate, 4 to 48 mg P04/m3. 



Apparently C. incisum is at home in oligotrophic 

 water. Ten of the thirty records of occurrence were in 

 water containing less than 10 mg P04/m3. Nielsen 

 (1934) classified this species as a surface species. In 

 the Carnegie collection it was found about equally at the 

 three levels (table 9). 



Table 9. Records of occurrence of C. incisum 

 at three levels 



A=Number of records. B=Per cent of total number of 

 samples collected at that depth. 



