CERATIUM SPECIES OF CARNEGIE COLLECTION 



31 



nets. Nevertheless, it was found more often in the net 

 than the piimp samples. There were thirty-three rec- 

 ords (16 per cent) for the net samples and twenty-seven 

 records (14 per cent) for the pump samples. 



Nielsen (1934) stated that C. azoricum is a typical 

 surface species but this is not confirmed by the Carne- 

 gie data (see table 28). There are not sufficient deeper 

 records, however, to warrant classifying C. azoricum as 

 a typical shade species. 



Table 28. 



Records of occurrence of C. azoricum Cleve 

 at three levels 



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

 samples collected at that depth. 



The ranges of environmental conditions in situ were: 

 temperature, 8.°2 to 29.°3 C; salinity, 32.7 to 36.0 per 

 mille; pH, 7.85 to 8.39; phosphate, 7 to 176 mg P04/m3. 



Only two of the sixty records of occurrence were 

 from water containing less than 10 mg P04/m3. 



34. Ceratium petersii Nielsen 

 Figure 16L, chart 26, appendix table 31 



As noted above, it is questionable whether this form 

 should be considered separate from C. azoricum Cleve 

 (see p. 30). For the present, however, it will be con- 

 sidered separately. Nielsen (1934) reported the species 

 from southeast of New Zealand. The records of Peters 

 (1934) for C. bucephalimi in the South Atlantic were re- 

 ferred to C. petersii bv Nielsen (1934), but the present 

 authors cannot agree with this (see below). The Carne- 

 gle records for C. petersii were at six stations, all in 

 the Pacific--five in the southeastern Pacific and one off 

 the west coast of the United States. Thus it is probable 

 that C. petersii is peculiar to the Pacific Ocean. 



Geographically it has been difficult to classify C. 

 petersii . partly because of the limited number of rec- 

 ords and partly because of Its peculiar distribution. It 

 is either cosmopolitan or subpolar. The surface tem- 

 peratures at its record stations varied from 16.°5 in the 

 South Pacific and 16.°4 in the North Pacific to 21. °2 off 

 Peru. It could be classified as subpolar except for its 

 peculiar distribution in the southeastern Pacific. No 

 other subpolar form has shown such a distribution. It 

 is tentatively considered to be a cosmopolitan species. 

 There is, of course, the possibility that C. petersii is a 

 cold-water subspecies of C. azoricum but this possibil- 

 ity is lessened by the fact that the typical C. azoricimi ls 

 also found in cold water. 



The total number of sample records for C. petersii 

 in the Carnegie collection was fifteen, of which ten were 

 rare, four occasional, and one common. Eight of the 

 records were from net samples and seven were from 

 pump samples. 



The ranges of environmental conditions in situ were: 



temperature, 10.°8 to 21.°2 C; salinity, 33.0 to 35.1 per 

 mille; pH, 7.68 to 8.18; phosphate, 12to233mgP04/m3. 



None of the records were in oligotrophic water. 



Nielsen (1934) found. the species only in the samples 

 from 50 to meters. In the Carnegie collections there 

 were six records for the surface, six for 50 meters, and 

 three records for 100 meters. Thus it is probably a sur- 

 face species. 



35. Ceratium arietinum Cleve 

 Figures 16A-K, chart 27, appendix table 32 



This species is one of the most ill defined of the 

 genus. It is composed of a great many variants, includ- 

 ing C. hur.ephaliiTTi which is here treated as a subspecies. 



Peters (1934) stated that in the Meteor material all 

 the variation forms described by Jorgensen (1911 and 

 1920) were foimd, but two forms were more common--a 

 small one and a large one. These intergraded but f. gracl- 

 lentum was distinct. 



The "large and small main form C. arietinum arie- 

 tinum " was found in various regions of the South Atlantic 

 but f . gracilentum was purely tropical, occurring between 

 latitudes 12° north and 10° south with water temperatures 

 over 22° C. 



Nielsen (1934) stated that he found only one form in 

 the South Pacific and that it corresponded to Jorgensen's 

 f. detortvun and f. gracilentum. Thus, apparently, Niel- 

 sen considered these two forms identical. 



The Carnegie collection is particularly rich in vari- 

 ations of this species. Only the more important of these 

 have been figured (figs. 16A-K). 



The characteristic arietinum has the apical horn dis- 

 placed to the left, whereas the right antapical horn is 

 strongly incurved (fig. 16E). In f. gracilentum Jorgensen 

 there is a distortion and lengthening of the apical horn, 

 which is sharply curved proximally (fig. 16K). Jorgensen 

 (1920) on the other hand, described a form, f. regulare .in 

 which the apical horn is symmetrically placed. This 

 form resembles C. bucephalum Cleve. 



In the present collection the placement of the apical 

 horn was extremely variable and showed transitions to 

 C. bucephalum (see figs. 16A-H). 



Nielsen (1934) classified Peters' (1934) southernform 

 of C. bucephalum as a new species, C. petersii. The 

 drawing of this species which Nielsen gives, however, is 

 quite different from the one given by Peters. In our opin- 

 ion these two forms cannot be included together. Peters' 

 figure (plate 3, fig. 16c) is truly a form of C. bucephalum . 

 which the authors have included as a subspecies of C. 

 arietinum. Nielsen's figure (fig. 44), however, is proba- 

 bly a distinct species as he indicated. It is closely re- 

 lated to C. azoricum (which see). 



The gracilentum form of the Pacific (fig. 16F) is dif- 

 ferent from that of the Atlantic (fig. 16K). The body is 

 not nearly so distorted, the antapical contour is more 

 nearly perpendicular to the axis of the apical horn, the 

 body is relatively wide, and the apical horn is not so ex- 

 tended. The transitions between gracilentimi and the typ- 

 ical arietinum. however, are continuous in both oceans. 

 It is very probable that several subspecies (in the 

 geographic sense) are concerned in the present complex. 

 Peters (1934) found f. gracilentimi to be limited to the 

 purely tropical waters between latitudes 12° north and 10° 

 south with temperatures over 22° C. In the Carnegie col- 

 lection this form was found farther north (to latitude 38.° 5, 



