1898.] PLANKTON OE THE FAEROE CHANNEL. 1021 



appear and disappear together in accordance with varying external 

 conditions. 



Only those species appear in the table, the horizons of which 

 seem to be in any way significant ; the horizons of the rest will be 

 simply recorded in the text. 



EADIOLARIA PEBIPYLAEIA. 

 THALASSICOLLA sp. 



A. number of specimens of this genus, taken chiefly at the 

 surface, could not be assigned with certainty to any species already 

 described. As with Collozoum, observations on living material 

 seem to be necessary in order to determine the specific position. 

 The following characters are enumerated here in order to assist 

 future recorders in identifying the form from this locality : The 

 striated calymma is very thick and colourless, the alveolar layer 

 internal to this is also very thick and colourless, with large alveoli ; 

 the extracapsular pigment is generally yellowish, occasionally 

 dark in colour; the central capsule is dark and considerably 

 thicker than in T. nudeata ; in specimens of which sections were 

 made, the membrane of the central capsule appeared to be divided 

 up into numerous small polygonal arese, with a single large pore 

 in the centre of nearly every area ; the nucleus is circular, with a 

 thickish nuclear membrane and irregular nucleolus ; intracapsular 

 inclusions ? 



The proportion of central capsule to nucleus, often utilized as 

 a specific character, does not appear to be trustworthy for this 

 purpose. The table below gives this proportion in a number of 

 specimens, apparently all referable to the same species : column I. 

 shows the total diameter in millimetres, arranged in order of size ; 

 column II. shows the diameter of the central capsule expressed as 

 a percentage of the total diameter. 



I. II. 



3-38 29 



3-29 19 



2-10 40 



1-96 21 



1-96 21 



1-90 30 



1-75 22 



1-70 22 



1-68 41 



1-61 21 



I. II. 



1-27 38 



1-26 33 



1-23 28 



Ml 33 



1-09 32 



1-09 32 



1-07 21 



93 37 



92 30 



77 26 



1-47 23 -63 36 



1-44 22 



The proportions of striated calymma, alveolar layer, and central 

 capsule showed similar variations. 

 It seems highly probable from the table that this Tkalassicolla is 



