THE PLANKTON OF THE FAROE CHANNEL AND SHETLANDS. 355 



3, Thalassiosolen atlanticus {nov. gemf.s et nov. sj).). 



In general appearance the animal resembles Th. nv.cleata, in the 

 possession of a vacuolated calymma and a central capsule surrounded 

 by black or dark brown pigment. This latter is very thick, and 

 extends between the extracapsular vacuoles in thick strands. The 

 calymma and vacuoles are otherwise like Tli. nucleata. The central 

 capsule shells out quite easily, and its investing membrane (which is 

 readily dissected off with needles) is much thinner than that of Th. 

 nucleata, but, like the latter, is perforated by multitudinous fine pores, 

 apparently more numerous than in Tli. nucleata, but showing on its 

 inner surface the same polygonal area markings as TJi. nucleata. 



A narrow space is observed all round the capsular contents and 

 just within the capsular membrane, in which I have been unable 

 to trace anything but oil globules. The whole of the centre of the 

 capsule is occupied by layers of radially disposed, rounded tubes, 

 closely packed in two (or three ?) layers converging towards the centre, 

 where their ends lie over and around the nucleus, without, however, 

 any intimate connection with the latter, and towards the periphery 

 branching into two, or sometimes three, club-shaped, closed ends. 

 Throughout the rest of their course they are usually quite straight, 

 and are rarely branched at their proximal ends. These tubes are 

 yellowish in colour, and appear to contain granules and irregularly 

 shaped bodies, which stain deeply with osmic acid. As they dissolve 

 completely in mineral acids they are not of siliceous nature. They 

 leave behind nothing but oil drops. With prolonged treatment by 

 caustic potash the contour of the tubes is not altered. Stained with 

 picrocarmine, the tubes are seen to be filled with granules deeply 

 stained and with clear spaces between them. Treat-ed with ether, 

 and subsequently stained with picrocarmine, the tube contents are 

 unaltered, except that the granules stain deeper than the rest. Osmic 

 acid stains them dark brown or black. They are not fat, and bear 

 a remarkable resemblance to the " assimilation plasma " of the 

 Collozoums. It is difficult to rupture the tubes, and they always 

 break transversely. The granules are arranged down the sides of 

 the tubes, apparently firmly adherent to the walls, and the lumen 

 of the tubes contains a clear space (? filled with fluid int/'a vitam). 



There do not appear to be any vacuoles in the central capsule, as 

 in other ThalassicoUidaj, but oil drops of irregular though often con- 

 siderable size occur between the tubes. 



The nucleus is round, and the investing membrane rather dense, 

 and it does not rupture easily. It is packed with small round 

 bodies, with a few of larger size, but contains no vacuoles. A few 



