DISTRIBUTION OF PHYTOPLANKTON 47 



C. concinnus, W.Sm. A single specimen of this typically northern diatom was met 

 with at WS 31. 



C. curvatulus, Gran, another northern form, common in Arctic seas, was recorded 

 at eleven stations but never in large numbers. Its distribution is shown in Appendix I ; 

 it will be seen that it occurred on both sides of South Georgia. 



C. excentricus, Ehr., was recorded in small numbers at four stations, all on the north- 

 eastern side of the island: Sts. 126, 127, 136 and WS 27. 



C. horridus, Karsten. Single specimens of this diatom were seen at two stations: 

 WS 34 and WS 35. 



C. kerguelenensis, Karsten, was recorded at fourteen stations but never in large 

 numbers. Its distribution is shown in Appendix I. 



C. lineatus, Ehr., was recorded in small numbers on each side of South Georgia. Its 

 distribution is shown in Appendix I. 



C. oculoides, Karsten, occurred in small numbers on each side of South Georgia ; its 

 distribution is shown in Appendix I. 



C. oppositus, Karsten?. A diatom having a general distribution around South Georgia 

 and at some stations taken in large numbers, was a form which we have provisionally 

 regarded as a variety of C. oppositus; although very likely it should be regarded as a 

 distinct species. Each cell possesses two apicules, one opposite or nearly opposite the 

 other; but there is only one to each valve, i.e. that of one valve is placed at the opposite 

 side of the disc to that of the other valve. In Karsten 's C. oppositus each valve has two 

 apicules, the ones of the upper and the lower valves lying one above the other and 

 opposite or nearly opposite those of the other side. Thus in our specimens one apicule 

 is absent from each valve. There is another important difference: the areoles are 

 arranged not in a simple radial fashion but placed in narrow fasciculae giving an 

 appearance not unlike that of C. filiformis, Karsten, although at times the fasciculae are 

 so narrow as to give the appearance of an almost simple radial arrangement as described 

 by Karsten for C. oppositus. The size of the cells and the form of the chromatophores of 

 our specimens agree with his C. oppositus. 



Whilst this diatom was common round South Georgia it was not found on the line 

 between South Georgia and the Falkland Islands. Its distribution is shown in Appendix I. 



C. quinqides-marcatus, Karsten. In the form as described by Karsten (1905) with 

 five apicules, it was recorded in small numbers at the following stations: 161, 

 WS 40, WS 67 and WS 68. At St. 44, a form was recorded having six apicules instead 

 of five and forms with seven apicules were met with at the following stations: 160, 

 WS 44, WS 45 and WS 67, whilst at the last-named station a single specimen having 

 eight apicules was also recorded. Among the unidentified species of Coscinodiscus we 

 have included one which agrees closely with C. quinqides-marcatus in both the sculptur- 

 ing of the valves and their concave surfaces, but differs in lacking the apicules entirely. 

 Since this species occurred at several stations with C. quinquies-marcatus and like it was 

 confined to the western side of South Georgia, it may be that it is yet another form of 

 the same diatom. Details of its occurrence are given under Coscinodiscus spp. 



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