i6 



STYLASTERIDAE 



Colour: white or faintly rose with strongly yellowish red gasterozooids. 



Occurrence: North Atlantic and west coast of Norway at depths from 100 to 1400111. 



Material : 



•'lugolf St. 15 66°i8' N., 25°59' W. 



— - 17 62°49' - 26°55' - 

 - 52 63°57' - i3°32' - 



— - 55 63°33' - i5°o2' - 

 "Thor" 1904 65°5o' - 26^53' - 



Hardanger Fjord 

 (G. O. Sars leg. 187 1) Storeggen (at Aalesund) 

 Trondhjeni Fjord . i 



Stylaster norvegicus is of coarser make than the preceding species (PI. II figs. 12— 15) and shows 

 no distinct main stem. Even the outermost tips of the branches may often be very thick (PI. II fig. 15) 

 and the cyclosystems show no regular arrangement as in our Eustylaster species. Nevertheless super- 

 ficial observation may easily confuse the species with colonies of the preceding species which are de- 

 formed by the numerous ampullae (cf. PI. II, fig. 11). — The branches in Stylaster norvegicus are often 

 flattened in the transverse plane of the colony. There is a marked difference between the front and 

 back, the number of cyclosystems being very greatly reduced on the back of the colony (PI. II 

 figs. 13 and 14). 



The cyclosystems are very regular in their formation in Stvlaster norvegicus. They are almost 

 circular and surrounded by a slightly raised ridge, which continues out into the septa between the 

 dactylopores. As the ampullae are very deeply immersed, their development causes no disturbance of 

 the regular form of the cyclosystems. In general there are 6 or 7, more rarely 8 quite separate dactylo- 

 pores round the open and deep gasteropore. The wall of the gasteropore shows an incision not specially 

 deep towards the dactylopore. — The short and broad gasterostyle is very characteristic; it is 

 approximately spherical and has almost the same breadth as height (PI. II fig. 23). The dactylostyles are 

 a little more prominent than in the two previous species, but they are also rather difficult to ob- 

 serve in Stylaster norvegicus. 



The ampullae are deeply imbedded in the branches and in general cannot be seen externally 

 on the colony; but branches with ampullae are on the whole thicker than sterile branches. — The 

 growth of the colony proceeds after the same type as in the Stylaster species already dealt with; 

 the concentric layers, which indicate a periodic growth in the colony, are also distinct here on thin 

 transverse sections of branches of the colony and are also readily seen in transverse series of sections 

 of branches which are freed from their calcareous substance. 



Whilst in the two preceding species we constantly find four tentacles on the gasterozooids 

 the innnber varies in .Stylaster norvegicus. As a rule the gasterozooid has 6 quite small tentacles, but 

 sometimes their number is reduced to 5 or increased to 7. The tentacles (Text-fig. D, PI. Ill fig.s. 27 and 31) 

 are also very small here; we might be inclined to call them rudimentary. The\- are also here the seat 

 of the small cnidocysts, which the gasterozooid is on the whole provided with. There is no reason 



