THE PLA.NKTON OF THE FAROE CHANNEL AND SHETLANDS. 353 



On other occasions what are probably very young individuals appear to 

 be without shell, and bear much resemblance to a Collozoum. The 

 number of the coronal spines round the pores of the shell varies con- 

 siderably, and it is probable that the Try])ano>i'ph(xra hrachys.i'plion n sjj. 

 briefly described by Cleve is really a Choenicosphsera. 



(3f the other Collosphferida I have found only shells of Acros2jhcvra 

 spinosa, never a colony. These have been brought up in the tow net 

 vertical hauls, on the west coast of Shetland, on three occasions. Its 

 appearance in this locality can be little more than accidental. The 

 shell is a perfect sphere with many short conical spines, rather broad 

 at the base, and tapering to a point and slightly curved. All the spines 

 are similar. They arise at the base from an upward process of shell at 

 the side of the pore, causing the base to appear as if perforated. The 

 pores are irregular in size, large and small being irregularly distributed. 

 The bars between the pores are three or four times the diameter of the 

 smaller of the latter. 



Diameter of the sphere, "21; length of spines, "002 mm.; width 

 of largest pore, about '0012 ; widest bars, "001 mm. 



The shell has much resemblance to Ac. ecldnoides (Haeckel), but 

 does not fully resemble either that or Ac. spinosa. 



THALASSICOLLIDA. 

 1. Thalassicolla nucleata. 



This is taken with great frequency in the surface tow net in the 

 coastal waters of Shetland and in the Faroe Channel, and I have 

 found it in quantities in the mid-water net at a depth of 40 to 

 50 fathoms. 



The organisms are, to the naked eye, little spherical balls of clear 

 jelly with a darkly pigmented centre, often densely black, less often 

 cinnamon-brown or yellow. The colour of the pigment is variable. 



The thick jelly calymma is characterised, as Hertwig remarked, by 

 (1) the richness in black pigment, (2) the numerous vacuoles. The 

 latter are small near the central capsule, larger towards the periphery. 

 The pigment is contained in a thick layer of the extracapsular sarcode 

 surrounding the central capsule, and is a dense layer of very small 

 round, black, or brown cells. From this layer it radiates in small 

 quantity through the protoplasmic strands which pass in all directions 

 between the vacuoles. Slight pressure of the cover glass is sufficient 

 to shell out the central capsule from the surrounding pigment layer. 

 It is surrounded by a firm membrane,* which on its inner side is 



* The dissection of this menibraue from the central capsule is very easily accomplished 

 without previous treatment of the specimen. 



