6 



CERATIUM m THE PACIFIC AND NORTH ATLANTIC OCEANS 



westward. It has two tongues extending westward, one 

 to the north, and one to the south of the Easter Island 

 Eddy. Although the temperatures vary a great deal in 

 this area, the water is everywhere eutrophic. The sur- 

 face temperatures vary from 14.°97 C at the southern- 

 most station to 27.°4 in the Panama region. The mean 

 phosphate content of the upper 50 meters is everywhere 

 above 25 mg P04/m3 and is above 50 mg at all stations 

 except those bordering the Easter Island Eddy. 



The waters of this region support a large plankton 

 population and, characteristically, few species are pres- 

 ent. Region V has been delimited by the points at which 

 the number of species per station rises above twenty. 

 Not only is the number of species lower in this region 

 than in the warmer tropical waters to the west, but the 

 composition of the Ceratixim flora is somewhat different. 

 The following tropical species found to the west were ab- 

 sent from region V. They are, significantly, all intoler- 

 ant tropical species. 



C. axiale 

 C. digitatimi 

 C. inf latum 

 C. reflexum 



C. cephalotum 



C. filicorne 



C. longirostrum 



The following species were found at fifteen or more 

 stations within the region. This list is composed mostly 

 of cosmopolitan and tolerant tropical species. 



C. candelabrum 

 C. contortum 

 C. furca 

 C. fusus 

 C. horridum 



v. horridum at twelve stations 



V. molle at five stations 



V. claviger at four stations 

 C. lunula 

 C. massiliense 

 C. pentagonum 



subsp. tenerum 

 C. tripos 



subsp. atlanticum at ten stations 



subsp. semipulchellum at fifteen stations 



The following species were found at five to fourteen 

 stations in the region. They are mostly slightly tolerant 

 tropical species. 



C. arietinum 

 subsp. arietinum at nine stations 

 subsp. gracilentum at three stations 

 subsp. bucephalum at three stations 



C. azoricum 



C. breve 



C. carriense 



C. concilians 



C. declinatum 



C. deflexum 



C. extensum 



C. gibberum 



C. gravidum 



C. hexacanthum 



C. llmulus 



C. macroceros subsp. gallicum 



C. ranipes 



C. symmetrlcum 



C. tenue 

 V. Inclinatum at four stations 

 V. tenuisslmum at two stations 



C. teres 



C. trichoceros 



C. vultur 



V. vultur at two stations 



V. pavillardii at two stations 



V. reversum at seven stations 



v. regular e at one station 



The following species were found at less than five 

 stations. They are notably almost all intolerant tropi- 

 cal species. 



C. belone 

 C. carnegiei 

 C. euarcuatum 

 C. incisum 

 C. longissimum 

 C. petersii 

 C. praelongumi 

 C. setaceum 



C. bohmii 

 C. compressum 

 C. falcatum 

 C. kofoidii 

 C. paradoxides 

 C. platycorne 

 C. pulchellum 

 C. subrobustum 



It is evident from the above lists that the most fre- 

 quent forms in region V are either cosmopolitan or tol- 

 erant tropical species. The intolerant tropical forms 

 are rarely collected in the region so they compose the 

 bulk of the list of rare forms. 



Richness of Species in Different Areas 



The well-known difference in number of species 

 found in cold and warm areas of the oceans is well illus- 

 trated by the Carnegie Ceratium data (see chart 53). In 

 the cold North Atlantic the number of species found at 

 each station was everywhere less than ten. This area 

 resembles the floristic region I, cold Atlantic. 



South of this area there is a transition zone in which 

 the number of species per station is between ten and 

 twenty. This lies in region II, the warm Atlantic region. 

 The rest of this region is characterized by high number 

 of species, more than twenty, except in the western part 

 of the North Equatorial Current, from longitude 40 ° west 

 to Panama, where the values were equal to that of the 

 transition zone, namely, between ten and twenty species 

 per station. 



In the Pacific the cold northern water is character- 

 ized by less than ten species per station. This area is 

 almost exactly like the floristic region IE, cold North 

 Pacific. At the southern limits of this area in both the 

 west and east there is a transition zone with values be- 

 tween ten and twenty species per station. 



These transitions lie within region IV, warm Pacific. 

 The rest of this region has more than twenty species per 

 station and, at some stations, more than thirty. 



In region V, southeast Pacific, the values are mostly 

 transitional in amount, namely, between ten and twenty 

 species per station. At one station west of the Panama 

 area (station 37) there were more than twenty species. 

 It is possible that this station has not been rightfully in- 

 cluded in region V but belongs to region IV, the warm 

 Pacific. The surface temperature at this station was 

 higher than at any other station in region V, namely, 

 27.°12 C. The area at this latitude between this station 

 and the central Pacific is unknown oceanographlcally and 

 planktologically so that it is not possible to say whether 

 station 37 lies in an eastern extension of region IV or 

 not. 



South of this station there were two stations at 

 which the number of species per station was less than 

 ten, stations 38 and 39. These were the only stations in 



